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New and Little-Known Gastropods From the Albian of the Mahajanga Basin, Northwestern Madagascar

Posted on: Monday, 15 May 2006, 12:05 CDT

By Kiel, Steffen

ABSTRACT-

Thirty-one gastropod species and one type of isolated larval shell are described from a quarry near Ambatolafia in the Mahajanga Basin, northwestern Madagascar. The ammonite fauna indicates a lower Albian age of the fauna (Cleoniceras besairiei Zone). The taxonomic position of the species described earlier is reviewed, incorporating new data on shell structure and protoconch morphology. Twelve species and one genus are new, with four species described in open nomenclature. The oldest hitherto known representatives of Cocculina sensu lato, Iphitus, Conjectura, Entomope, Tomura, and possibly Vatopsis and Paladmete, are described. Nacre is documented in a species of Semisolarium, providing further evidence for the position of this genus within the Vetigastropoda. Eight of the species occur also in the Cretaceous of Europe or are tentatively assigned to European species. Three species have close relatives in the Aptian/ Albian of Japan, one species may have relations to the Albian of Texas. The new genus is Mahajangina (family uncertain) for a species having a small, trochispiral teleoconch with spines on the periphery, and a conical, bicarinate larval shell. The new species are: Cirsocerithium collignoni, Zardinistylus betsibokaensis, Pommerozygia mahajangensis, Conjectura minuta, Buvignieria berwaldi, Mahajangina weitschati, Entomope crassilabrum, Paladmete? rasoarinoroae, Tomura ambatolafiensis, Carinathilda parviruga, Carinathilda bandeli, and Gymnothilda pagodoidea.

INTRODUCTION

IN 1949 the French Gnral Maurice Collignon published an account of Albian fossils from the Mahajanga Basin given to him by H. Besairie and V. Hourcq (Collignon, 1949). The localities fell into oblivion until they were rediscovered a few years back by French- Madagascan ammonite traders. Since then, ammonites with original nacre shimmering in blue, green, and red have flooded the markets. With the aid of these ammonite traders it was possible to visit one of the localities and to collect material for scientific investigations. Because of the excellent preservation of the material, Collignon's work on the gastropods can be evaluated using additional evidence from protoconch morphology and shell ultrastructure, allowing description of 12 new species and four in open nomenclature.

GEOLOGICAL SETTING AND STRATIGRAPHY

The investigated locality is situated near the top of an escarpment 3 km to the west of the village of Ambatolafia in the Mahajanga province in northwestern Madagascar (Fig. 1). Here a long quarry was dug along the escarpment by local villagers searching for ammonites. The ammonites are found in the hard, basal glauconitic sandstone layer, which is 15-20 cm thick. Gastropods and bivalves of moderate size (up to 5 cm) are also abundant in this layer. This layer is referred to as the "ammonite bed" in the following text. Above the ammonite bed follows a nearly 15 cm thick layer of dark gray, glauconitic siltstone. Larger fossils are rare in this layer, only few gastropods and bivalves reach 1 cm, but microfossils are abundant. This layer is referred to as "microlbssil bed" in the following text. The microfossil bed is succeeded by a homogenous, gray siltstone without visible macrofossils. The observed maximum thickness of this layer is 10 in. Stratigraphically the fauna belongs to the Cleoniceras bexairiei Zone of the lower Albian (Collignon, 1963).

MATERIAL AND METHODS

Samples from the microfossil bed were processed with a 5%-10% H^sub 2^O^sub 2^ solution using standard procedures. Samples from the ammonite bed were dried and treated with a saturated Glaubers salt solution. The processed samples were then washed through sieves with mesh sizes of 2, 1, 0.5, 0.2, and 0.064 mm. Gastropods were only picked from the 2, 1, and 0.5 mm fractions. Samples were mounted on stubs, coated with gold, and photographed using a Leo 1455VP scanning electron microscope. Measurements with this machine show a range of variation of about 3% while using different working distances and virtual rotation, so only approximate values are given here. Macrolossils were photographed with a Leica SL2 and an Olympus Camedia C-3040 Zoom digital camera. The material is deposited in the Museum fur Naturkunde, Berlin, Germany.

ECOLOGIC AND BIOGEOGRAPHIC NOTES ON THE FAUNA

The gastropods presented here are from the Cleoniceras besairiei Zone of the lower Albian (Collignon. 1963) and are therefore slightly older than those described by Collignon (1949) from Ambarimaninga. The Ambarimaninga fauna, from the Lcmtirocci'as sputhi Zone, was considered basal middle Albian age (Owen, 1971) and. among the macrotbssils. contains two further species which I did not find in the quarry at Amhatolalia: /-Vwsarus besuiriei Delpey. 1948 and Eiicheliis lenohlci Collignon. 1949. The Ambarimaninga fauna, however, lacks the conspicuous Paladmi'te'l rasoarinoroae n. sp. of the Ambatolafia fauna. Whether this difference results from the slightly younger stratigraphic age of Collignon's fauna, or from a difference in facies, is unclear. The rare and very small species that make up a large portion of the fauna described here cannot be included in a comparison with Collignon's fauna, first because it is likely that they were not preserved in the hard glauconitic sandstone that yielded his material, as evident by the rarity of microfossils in the ammonite bed in Ambatolafia: and second, Collignon did not have the technical possibilities (e.g.. SEM) to document such minute species. However, nine species are shared between Collignon's middle Albian fauna and the early Albian fauna of Amhatolafia. indicating that these species had a time range of at least four million years.

The microfossil bed contains 25 gastropod species. 17 of which occur only in this bed. The ammonite bed contains 14 species, of which 8 occur only in this bed (see Appendix). Because most of the species that are restricted to the microfossil bed are minute, this restriction might, at least partly, be a preservation artifact. Of ecological significance is the following observation: all but one species from the microfossil bed had a planktotrophic vcliger larva (exception: Cocciilina sp.). and the majority of the specimens apparently died as juveniles, or even as larvae [e.g., Latiala besairiei (Collignon, 1949)]. This indicates that living conditions might have deteriorated here occasionally. In contrast, most of the specimens from the ammonite bed were adults.

Comparisons with other faunas of the same age have to be regarded with caution. Twenty-three out of 31 species and one genus occur exclusively in the Mahajanga Basin, superficially indicating a high degree of endemism. However, many of the species are small to minute, which makes it likely that they are not preserved or have been overlooked in other places.

Eight of the species described here from the Mahajanga Basin occur also in the Early Cretaceous (Valanginian-Albian) of Europe or are tentatively assigned to European species of that age (see Appendix). Of these, Ringinella lacryma d'Orbigny, 1842, Ampullina gaultina (d'Orbigny, 1842), and Metacerithium trimoline Michelin, 1838 occur in the Albian of the Paris Basin, the latter two also in the Albian of the Mediterranean Basin in France (d'Orbigny, 1842). The Ambatolafia fauna shares Tessarolax retusa (Sowerby, 1836), Metacerithium trimoline, and Ringinella lacryma with the Gold clay in southern England (Smart et al., 1966), and Ampullina gaultina and Tessarolax retusa with the lower Albian fauna of northern Germany (Wollemann, 1900, 1908).

No species are recognized as being in common with other regions of the world, however, closely related species occur. From the Aptian/Albian of Japan, Kase ( 1984) described three species that are apparently very similar to those of the Mahajanga Basin: Gyrodes munitus (Forbes, 1846) to Ampullina gaultina, Latiala hayamii Kase, 1984 to L. besairiei, and Cirsocerithium subspinosum Deshayes, 1842 to C. collignoni n. sp. The Central American/Caribbean and North American Gulf Coast faunas of Albian age have a rather Tethyan/ carbonate facies character (Stanton, 1947; Sohl, 1971; Akers and Akers, 1997). Only Cerithium diversecingulatum Stanton, 1947 might be related to Metacerithium aff. trimoline Michelin, 1838, but this assumption needs confirmation by reinvestigation of Stanton's material.

SYSTEMATIC PALEONTOLOGY

Class GASTROPODA Cuvier, 1797

Subclass COCCULINIFORMIA Haszprunar, 1987

Family COCCULINIDAE Dall, 1882

Genus COCCULINA Dall, 1882

Type species.-Cocculina rathbuni Dall, 1882; Recent, Barbados Island, Caribbean Sea.

COCCULINA sensu lato sp.

Figure 2.1-2.5

Description.-Protoconch comprising little more than half a whorl; apical fold broad and short; surface pitted; about 156 m wide; tip of protoconch not immersed in posterior slope of teleoconch. Teleoconch limpet-shaped, oval in outline; anterior slope convex, posterior slope more-or-less straight; with sculpture of fine, commarginal cords or growth lines. Incomplete specimen 888 m long, 886 m wide, and 710 m high. Shell about 50 m thick, of simple crossed-lamellar or intersected crossed platy structure.

Material examined.-One specimen from the microfossil bed, MB.Ga.1787.

Occurrence.-Albian, Mahajanga Ba\sin, Madagascar.

Discussion.-This species is placed within the Cocculinidae due to the short, broad apical fold of the protoconch. Recent Cocculinidae have a netlike or commarginal sculpture on the protoconch (McLean and Harasewych, 1995), but this is absent from the species described here. It is therefore assigned to Cocculina s.l. only. Simple crossed-lamellar and intersected crossed platy shell structure were described also for four extant cocculiniforms (Hedegaard, 1990; Kiel, 2004). This character distinguishes Cocculina s.l. sp. from docoglossids with convergent shell morphologies. The Cocculiniformia have been traced back into the Eocene (Marshall, 1994), but this group is likely to have a much longer fossil history (Haszprunar, 1998). The species reported here represents the oldest record of this group.

FIGURE 1-The fossil locality in the Mahajanga province, northeastern Madagascar.

Subclass VETIGASTROPODA Salvini-Plawen, 1980

Family PLEUROTOMARIIDAE Swainson, 1840

Genus LEPTOMARIA Deslongchamps, 1864

Type species.-Trochus amoena Eudes-Deslongchamps, 1849; Middle Jurassic (Bajocian), France.

LEPTOMARIA MAGNETI Collignon, 1949

Figure 2.6-2.8

Leptomaria magneti COLLIGNON, 1949, p. 33, pl. 5, fig. 13.

Description.-One whorl preserved, trochiform, almost straight- sided, selenizone about in the middle of the whorl, spiral and axial sculpture fine, basal margin sharp, base with spirals only; umbilicus about one-quarter diameter of last whorl; conical, axial sculpture dominant, spirals present; aperture trapezoid, inner lip thickened. Shell structures from outside to inside: simple prismatic, columnar nacre. Incomplete shell 38.0 mm in diameter, height 18.0 mm.

Material examined.-One specimen from the ammonite bed, MB.Ga.1788.

Occurrence.-Albian, Mahajanga Basin, Madagascar.

Discussion.-The composition of shell structures present in Leptomaria magneti was also described for late ontogenetic whorls of extant pleurotomariids (Erben and Krampiz, 1972; Harasewych, 2002), as well as Carboniferous pleurotomariids (Batten, 1972).

Family DISCOHELICIDAE Schroder, 1995

Genus DELPEYA Collignon, 1949

Type species.-Delpeya cottreaui Collignon, 1949; Early Cretaceous (Albian), Mahajanga Basin, Madagascar.

Diagnosis.-(Collignon, 1949, p. 32, my translation): "Early whorls planispiral, later the shell becomes helicoidal in shape. The base is concave and has a deep and conical umbilicus. Ornamentation of ribs, varices and spines. There are no keels, and the growth lines are fine and radial." Based on the newly collected material, it can be added that the protoconeh is tightly coiled, and that homogenous, columnar nacreous, simple prismatic, and intersected crossed platy structure is present in its shell.

Discussion.-Collignon (1949) placed Delpeya near Discohelix Dunker, 1848 among the Euoniphulidae Koninck. 1881. Bandel and Fryda (1998) showed that the Euomphalidac belong to their own subclass among the Gastropoda due to their openly coiled protoconchs [see Ntzel (2002) for a different view]. Delpeva cottreaui has a tightly coiled, archaeogastropod-type protoconeh. and it has a nacreous layer in its shell. Among the Gastropoda, nacre is known only from the Vetigastropoda (Hedegaard, 1990; Hickman and McLean, 1990). Delpeya can thus be placed among the Vetigastropoda. Delpeva is considered to have been derived from Jurassic genus Nummocalcar Cossmann. 1896 (Kiel and Bandel. 2004), and as a member of the Discohelicidae due to similar sculpture and planispiral coiling of the early whorls. Similar shells arc also built by members of the extant turbinid subfamily Angariinae Thiele, 1924. Two further species are included in Delpeya: D. dtipiniana (d'Orbigny, 1842: pl. 182, figs. 1-4) from the Hauterivian of France which has axial ribs on the periphery of the last whorl, and D. hilpeni Kiel and Bandel, 2004 from the Cenomanian of Germany, which has commarginal rings around its whorls. Delpeya thus ranges from Hauterivian to Cenomanian.

DELPEYA COTTREAUI Collignon, 1949

Figure 2.9-2.15

Delpeya cottreaui COLLIGNON, 1949, p. 32. pl. 5, figs. 10-12.

Description.-Protoconeh composed of half a whorl, about 260 m wide. Teleoconch euomphaloid, spire flat to slightly erected, seven to eight whorls, sutures deep; whorls roundish, upper side flat, with four beaded spiral cords; peripheral angulation with spines, about every third to fifth spine more strongly developed then those in between: outer side convex, bearing seven to eight beaded spiral cords; spines on basal angulation correspond with those of peripheral angulation; umbilicus wide, conical, bearing two spiny keels on each whorl. Shell structures from outside to inside: homogenous, columnar nacre, simple prismatic, intersected crossed platy, simple prismatic. Figured specimen 24.0 mm in diameter, height 10.0 mm.

Material examined.-Twenty-three specimens from the ammonite bed. figured specimens MB.Ga. 1789-91. remaining species MB.Ga. 1855.

Occurrence.-Albian, Mahajanga Basin, Madagascar.

Family TROCHIDAE Rafinesque, 1815

Subfamily MARGARITINAE Stoliczka, 1868

Genus SEMISOLARIUM Cossmann, 1916

Type species.-Solarium monilifenim Michelin, 1838; Early Cretaceous, France.

Discussion.-Kase (1984) discussed the history and relationships of Semisolarium more extensively and concluded that it should be placed within the Margaritinae due to its similarities to Atira Stewart, 1927. The archaeogastropod-like protoconeh and the nacreous shell documented here confirm the position of Semisolarium within the Vetigastropoda. and Kase's (1984) treatment is followed.

SEMISOLARIUM BASSAE (Collignon, 1949)

Figures 2.16-2.18, 3.1-3.3

Solarium bassae COLLIGNON, 1949, p. 35, pl. 5. fig. 15.

Description.-Protoconch composed of three-quarters of a whorl, smooth. 220 m wide. First three teleoeoneli whorls convex, smooth, then two nodular keels develop at suture: lower keel developing into a strong, raised keel producing a deep suhsutural groove. Keel and groove flatten after one-and-a-half whorls, groove developing into a ramp on which five additional nodular spirals appear: also below the main keel nodular spirals and a basal keel appear. Base slightly convex, with 18 spiral cords and sinuous radial ribs: umbilicus about one quarter of diameter of last whorl, with bicarinate keel inside: aperture rhomboid, inner Hp callused. Shell structures from outside to inside: simple prismatic, columnar nacre, intersected crossed platy. simple prismatic. Figured specimen (2.16-2.18) 11.0 mm high, width 12.0 mm.

Material examined.-Fifty-two specimens from the ammonite bed, figured specimens MB.Ga. 1792-94, remaining specimens MB.Ga.1856.

Occurrence.-Albian, Mahajanga Basin, Madagascar.

Discussion.-The development of the strong keel and suhsutural groove for about one and a half whorls has been observed in all examined specimens, but differs greatly in intensity. Collignon (1949) assigned this species to Solarium Lamarck. 1799 (=Architectonica Ro'ding, 1798). However, architectonicids have a large, sinistrally coiled protoconch (Bieler. 1993) in contrast to the dextrally coiled, archaeogastropod-type protoconch of Semisolurinm hassae. Additionally, nacre does not exist among architectonicids (Bandel, 1990; Cranosolariinn cretastcum Stilwell and Henderson. 2002 with nacreous shell from the Australian Cenomanian is a vetigastropod).

Subclass CAENOGASTROPODA COX, 1959

Family AMPULLINIDAE Cossmann, 1918

Genus AMPULLINA Bowdich, 1822

Type species.-Ampullaria depressa Lamarck, 1804; Eocene, France.

AMPULLINA GAULTINA (d'Orbigny, 1842)

Figure 3.4. 3.5

Natica gaultina D'ORBIGNY, 1842, p. 156. pl. 173. ligs. 3. 4; WOLLEMANN, 1906, p. 287, pl. 10. fig. 1.

Gyrodes aff. tenellus STOLICZKA, 1868. COLLIGNON, 1949. p. 30, pl. 5, fig. 6.

Description.-Protoconch unknown. Teleoconch gyrodiform, spire pointed-conical, whorls expanding rapidly in size; early whorls conical, later whorls with broad suhsutural ramp and groove, periphery convex; growth lines sinuous at ramp, strongly oblique at periphery: aperture large, elongate-oval, inner lip straight and smooth: umbilicus narrow to moderately wide, smooth, umbilical margin with weak ridge. Figured specimen 28.0 mm high and wide, largest specimen 43.0 mm high, 48.0 mm wide.

Material examined.-Eleven specimens from the ammonite bed, figured specimen MB.Ga. 1795. remaining specimens MB.Ga.1857.

Occurrence.-Albian. Mahajanga Basin. Madagascar: Aptian/ Albian of Western Europe.

Discussion.-This species is placed here in the Ampullinidae rather than the Naticidae Forbes. 1838 as done by Collignon (1949). firstly because it shows umbilical features characteristic of ampullinids (Kase and Ishakawu, 2003), and secondly because drill holes in molluscan shells as produced by extant naticids were not found in shells from the ammonite bed at Ambatolafia.

FIGURE 2-Albian gastropods from northeastern Madagascar. 1-5, Cocculina sensu lato sp., MB.Ga. 1787. microfossil bed; 1-3, adult shell, length 0.88 mm, 50, 4, protoconch, 230, 5, shell structure, 750, 6-8, Leptomaria magneti Collignon, 1949, MB.Ga.1788, ammonite bed; 6, 7, fragment of adult shell, diameter 38 mm, 1.2, 8, close- up on the nacreous shell, 1,500, 9-15, Delpeva cottreaui Collignon, 1949; 9-11, adult shell, MB.Ga.1789. ammonite bed, diameter 24 mm, 2, 12, protoconch, MB.Ga.1790, ammonite bed, 90, 13, cross section of shell showing distribution of shell structures, MB.Ga.1791, ammonite bed, 85, 14, close-up on nacre, 1,500, 15, close-up on intersected crossed platy structure, 750. 16-18, Semisolarium bassae (Collignon, 1949), MB.Ga.1792. ammonite bed, adult shell, diameter 12 min, 4.

Family CAMPANILIDAI; Douvill, 1904

Genus METACHRITHIUM Cossmann, 1906

Type species.-Cerithiuni trimonile Michelin, 1838; Early Cretaceous (Albian), France.

METACERITHIUM aff. TRIMOLINE Michelin, 1838

Figure 3.6-3.10

Cerithium (Metacerithium) sp. aff. trimonile MICHELIN, 1838. COLLIGNON, 1949, p. 37, pl. 4, f\igs. 16-21.

Description.-Protoconch globular, two-and-a-quarter whorls, about 330 m wide and 370 m high; embryonic part about 115 m wide, sculptured with fine nodules, suture with larval shell prosocyrt; larval whorls convex, with fine, irregular or collabral nodules, suture with adult shell with a prominent varix on the upper half of the whorl, a rib on the lower half, and a narrow larval hook. Teleoconch turriculate, of numerous whorls; first four whorls with varixlike, opisthocyrt ribs crossed by six fine spiral threads that disappear afterwards; ribs then thicken basally, and eventually change into a tuberculate keel, on thirteenth whorl two more tuberculate spiral cords appear above the tuberculate keel; aperture oval, columella smooth, anterior end with short siphonal canal. Figured adult shell 8.0 mm high.

Material examined.-More than 300 specimens from the microfossil bed (MB.Ga. 1858) and 10 specimens from the ammonite bed (MB.Ga.1859). figured specimens MB.Ga.1796-98.

Occurrence.-Albian, Mahajanga Basin, Madagascar; possibly Albian of Western Europe.

Discussion.-This species is only hesitantly assigned to Melacerilhium trimoline (following Collignon in this regard) because the development of the early sculpture differs in some respects from the description of Abbass (1973). However, Abbass (1973) admitted some variation in the sculptural patterns, and his observations were based on light microscopy, not on scanning electron microscopy. Thus some very fine features may have been overlooked or misinterpreted. The protoconch of Metacerithium ponsi Kiel and Bandel (in Kiel et al., 2000) is of similar shape but is too poorly preserved to show microsculpture or detailed apertural features. Such features are not known from other campaniloids (Houbrick, 1989; Kiel et al., 2000). The Valanginian Dzikella trainmen Kaim, 2004, type species of Dzikella Kaim, 2004. has a very similar protoconch and also a similar teleoconch. However, that species is known from juveniles only, and might be congeneric with Metacerithium. Kaim (2004) pointed out similarities of Dzikella to the Valanginian Diatrypesis kurushini Kaim, 2004. The protoconch of that species is more dome- shaped than those of Metacerithium and Dzikella, but the teleoconch resembles that of campanilids, especially regarding the strongly beaded subsutural belt and its growth lines. However, the strong subsutural belt of certain species of Campanile Fischer, 1884 develops only after a fair number of whorls (the initial teleoconch whorls have keels, see Kiel et al., 2000). and Diatrypesis kurushini is known from juveniles only, thus any speculation about its systematic position is premature.

Family PROCERITHIIDAE Cossmann, 1906

Genus CIRSOCERITHIUM Cossmann, 1906

Type species.-Cerithium subspinosum Deshayes in Leymiere, 1842; Early Cretaceous, France.

CIRSOCERITHIUM COLLIGNONI new species

Figure 3.11-3.14

Cerithium subspinosum Deshayes in Leymiere, 1842. COLLIGNON, 1949, p. 36, pl. 4, figs. 14, 15.

Diagnosis.-Cirsocerithium with large, bicurinate protoconch comprising five-and-a-half volutions: teleoconch with six volutions, sculpture of three major spirals and 14-16 axial ribs per whorl: inside of outer lip with up to live small denticles, outside thickened by a varix.

Description.-Protoconch conical, five-and-a-half volutions, with large larval hook, height about 900 m, width about 720 m; embryonic part about 100 m wide, smooth; larval whorls with a subsutural row of tubercles, two tuberculate keels, and one basal keel, basal keel often covered by succeeding whorl: larval hook large. Teleoconch cerithioid, of six convex whorls with three major spiral cords, up to two minor ones below, one subsutural spiral cord, three fine spiral threads on the subsutural ramp, and 14-16 axial ribs; on later whorls a line spiral line appears between each of the three major spiral cords: basal margin sharp, base concave, with 10 spirals; aperture subcircular, anterior canal bordered by two denticles: one each on columella and base: inner lip strongly callused, inside of outer lip with up to five small denticles, outside thickened by a varix. Figured adult shell 9.0 mm high.

Etymology.-Named in honor of Maurice Collignon, for his work on Madagascar) fossils.

Types.-Holotype MB.Ga. 1799. microfossil bed: paratype MB.Ga.1800. microfossil bed.

Other material examined.-More than 300 specimens from the microfossil bed (MB.Ga.1860) and 30 specimens from the ammonite bed (MB.Ga.1861).

Occurrence.-Albian, Mahajanga Basin. Madagascar.

Discussion.-Collignon (1949) assigned this species to Cerithium siibspinostim Deshayes. Deshayes (in Leymiere. 1842, p. 14, pl. 17. fig. 12), as well as d'Orbigny (1842-1843. p. 364, pl. 229. figs. 4- 6) and Kase (1984. p. 130. pl. 20. figs. 10. 11). described 11 axial ribs per whorl for C. subspinosum, so this character seems quite constant. Collignon's and my specimens of the Madagascan species, however, have 14-16 ribs per whorl. Based on this difference, the new name Cirsocerithiiun collignoni is introduced for this species, and it is assigned to Cirsocerithiiun due to its strong similarity to Cirsocerilhium suhspinosum. type of the genus. Two Valanginian species from Poland are very similar to Cirsocerithiiun collignoni: Proccrithiiun kulickii Schroder, 1995 and P. tricuspis Schroder. 1995. regarding their very large protoconchs and broadly conical teleoconchs. Both species were placed in Cryptaulax Tate, 1869 Kaim (2004, p. 42), who considered them "more similar to each other than to other members of the genus" and suggested they "possibly represent a derived lineage evolved from the Cryptaulax stem." This derived lineage could indeed be Cirxocerithium, and Procerithium kulickii and P. tricuspis are transferred here to Cirsocerithium.

FIGURE 3-Albian gastropods from northeastern Madagascar. 1-3, Seniixolarium bassae (Collignon, 1949); 1, juvenile shell showing early ontogeny of sculpture, MB.Ga.1792, ammonite bed, width 3.7 mm, 15. 2, protoconch of same specimen as 1, 150, 3, close-up on nacreous shell, MB.Ga.1794, ammonite bed, 1,600. 4, 5, Ampullina gaultina (d'Orbigny, 1842), MB.Ga.1795, ammonite bed, height 28 mm, 2. 6-10, Metacerithium cf. trimoline Michelin, 1838; 6, juvenile shellm MB.Ga.1797, microfossil bed, height 1.6 mm, 50, 7, embryonic shell, same specimen as 6, microfossil bed, 360, 8, close-up on fine tuberculate sculpture on protoconch, same specimen as 6, 680, 9, close-up on protoconch, same specimen as 6, 110, 10, telcoconch, apertural view, MB.Ga.1796, ammonite bed, height 8.0 mm, 10, 11-14, Cirsocerithium collignoni n. sp.; 11, holotype, MB.Ga.1799, microfossil bed. height 9.0 mm, 9, 12, paratype, MB.Ga.1800. microfossil bed, juvenile shell showing the large protoconch with larval hook, height 1.6 mm, 50, 13, embryonic shell, same specimen as 12, 300, 14, sculptural delail of the proloconch, same specimen as 12, 80.

Family PSEUDOMELANIIDAE Hrnes, 1884

Genus PSEUDOMELANIA Pictet and Campiche, 1862

Type species.-Pseudomelania gresslyi Pictet and Campiche, 1862; Cretaceous, France.

PSEUDOMELANIA? cf. REQUIENIANA (d'Orbigny, 1842)

Figure 4.1

?Eulima requienianu D'ORBIGNY, 1842, p. 67. pl. 155, fig. 18.

Description.-Two teleoconch whorls, suture indistinct, surface very weakly convex, smooth except for very fine, slightly sinuous growth lines; aperture lenticular, parietal lip with thin callus, columclla with numerous oblique, line spiral threads; outer lip with two bulges. Incomplete shell 14.0 mm high, width 7.0 mm.

Material examined.-One specimen from the ammonite bed, MB.Ga.1802.

Occurrence.-Albian, Mahajanga Basin. Madagascar; possibly Turonian, Uchaux Basin, France.

Discussion.-This specimen resembles d'Orbigny's illustration of Eulima reqiiieniana (here placed in Pseudoinelania). but with only one fragment with broken aperture available it cannot be assigned to Pseudoinelania requieniana with any certainty.

Family ZYGOPLEURIDAE Wenz, 1938

Genus ZARDINISTYLUS Bandel, 1991

Type species.-Coelochrysalis misurinensis Zardini, 1978; Triassic, St. Cassian Formation, Italy.

ZARDINISTYLUS BETSIBOKAENSIS new species

Figure 4.2, 4.3

Diagnosis.-Protoconch conical, of three-and-a-half whorls, subsuturally constricted axial ribs on the apical half of whorls; teleoconch slender turriculate, whorls slightly convex, nine to ten varixlike axial ribs per whorl.

Description.-Protoconch conical, three-and-a-half whorls, axial ribs on the apical half of whorls, constricted at suture, growth lines strongly sinuous below ribs, protoconch about 530 m high and about 375 m wide. Teleoconch slender turriculate. four-and-a-half whorls, whorls slightly convex, nine to ten varixlike axial ribs with interspaces about twice as wide as ribs; basal margin well rounded, aperture rounded rhomboid, columellar and parietal lips callused. Holotype 2.0 mm high, 0.7 mm wide.

Etymology.-For the Betsiboka River, which runs through the Mahajanga Basin.

Type.-Holotype MB.Ga. 1803, from the microfossil bed.

Other material examined.-Ten specimens from the microfossil bed (MB.Ga.1862).

Occurrence.-Albian, Mahajanga Basin. Madagascar.

Discussion.-This species differs from the two Triassic species of Zarilinisfylus by its less constricted basal margin and by its callused parietal lip. Although Zardinistylus betsibokaensis has all characteristics of Zardinistylus it should be noted that no Jurassic representative of this genus has been reported.

Family POMMEROZYGIIDAE Grndel, 1999

Genus POMMEROZYGIA Grndel, 1998

Type species.-Pommerozygia ueckeritzensis Grndel, 1998; Jurassic (Callovian), northern Germany.

Discussion.-Grndel (1998) erected the two very similar monotypic genera Erratopleura Grndel. 1998 and Pommerozygia, considering them distinct based on the lack of callus on the inner lip of the aperture of Pommerozygia, which is present on Erratopleura. and the lack of nodular sculpture on the protoconch of Er\ratopleura, which is present in Pommerozygia. The two species described below have both nodular sculpture on the protoconch and callus on the inner lip. As first reviser, I synonymize Erratopleura with Pominerozvgid, although Erratozvga was the first of the two genera to be introduced by Grndel (1998). to maintain consistency with the family name Pommerozygiidae.

POMMEROZYGIA aff. ALBENSIS (d'Orbigny, 1842)

Figure 4.4-4.7

?Eulima albensis D'ORBIGNY, 1842, p. 64, pl. 155, figs. 14, 15.

Description.-Protoconch dome-shaped, three-and-a-quarter whorls, about 470 m wide and about 400 m high; embryonic part about 73 m wide; larval whorls with sinuous, collabral ribs, ribs prominent at suture, faint below; suture with teleoconch marked by a sinuous thickening. Teleoconch elongate, smooth, straight-sided, suture indistinct, growth lines slightly prosocyrt; basal margin rounded, base with line spiral threads; aperture with thin inner lip, base well rounded, apical side tapering. Shell 2.7 mm high, width about 0.9 mm. apical angle 16.

Material examined.-One specimen from the microfossil bed, MB.Ga.1804.

Occurrence.-Albian, Mahajanga Basin, Madagascar; possibly Hauterivian, France.

Discussion.-D'Orbigny (1842) reported Eulima albensis from the "Neokomian" of Marolle, which refers to the Hauterivian of Marolles- sous-Lignihres (H. A. Kollmann, personal commun., 2002). The teleoconch of d'Orbigny's species is indistinguishable from that of my specimen, but because the protoconch of d'Orbigny's species is unknown, and due to its slightly older age. the Madagascan species is only tentatively assigned here. It is placed within Pommerozvgia due to its slender, smooth teleoconch combined with a dome-shaped protocoiich having nodular subsutural ribs, characteristic for Pommerozygia. Protoconchs of the Eulimidae, in contrast, are pointed- conical and smooth (Bouchet and Warn, 1986: Warn, 1992).

Pommerozygia mahajangensis can be distinguished from P. aff. albensis by the more convex teleoconch whorls and the row of line tubercles on the protoconch of P. mahajangensis, whereas P. aff. albensis has subsuturally constricted ribs on its protoconch. The Jurassic species P. ueckeritzenxis and P. piehli (Grndel, 1998) both differ from the two species described here by having more convex whorls.

FIGURE 4-Albian gastropods from northeastern Madagascar. 1, Pseudomelania cf. requieniana (d'Orbigny, 1842), MB.Ga.1802, ammonite bed, height 14 mm, 4. 2, 3, Zardinistylus betsibokaensis n. sp., holotype, MB.Ga.1803, microfossil bed, height 2.0 mm, 2, apertural view, 35, 3, protoconch, 120. 4-7, Pommerozygia aff. albensis (d'Orbigny, 1842), MB.Ga.1804, microfossil bed, height 2.75 mm; 4, 5, apertural and side view, 25, 6, 7, apical and side view on protoconch, 100. 8-12, Pommerozygia mahanjangensis n. sp.; 8, spire of holotype, MB.Ga.1805, microfossil bed, height 4.5 mm, 20, 9, last whorl of holotype, showing thickened aperture, height 2.9 mm, 20, 10, apertural view on paratype, MB.Ga.1806, microfossil bed, height 1.5 mm, 40, 11, 12, paratype, close-up on protoconch, 125. 13, Vatopsis? sp., MB.Ga.1808, microfossil bed, height 0.9 mm, 60. 14- 16, Opaliopsis franciscae (Collignon, 1949); 14, juvenile shell with protoconch, MB.Ga.1812, microfossil bed, height 3.0 mm, 30, 15, fragment of teleoconch, MB.Ga.1810, ammonite bed, height 14.0 mm, 4, 16, larger fragment of teleoconch, MB.Ga.1811, ammonite bed, height 41.0 mm, 1.5.

POMMEROZYGIA MAHAJANGENSIS new species Figure 4.8-4.12

Diagnosis.-Protoconch conical to dome-shaped, of three whorls, with fine subsutural tubercles; teleoconch slender turriculate, whorls weakly convex, smooth: aperture apically pointed, outer and basal lip thickened.

Description.-Proloconch conical to dome-shaped, of three whorls, about 320 m high and 370 m wide; embryonic part about 120 m wide, smooth; larval whorls smooth apart from collabral growth lines and line subsutural tubercles, suture with adult shell formed by a thin, opisthocyrt edge. Teleoconch highspired, elongate; whorls weakly convex, smooth, growth lines straight, faint; fine incised spirals between the growth lines just above the aperture, aperture apically pointed, outer side rounded, inner lip little reflected, callused. outer and basal lip thickened. Holotype (complete) 8.4 mm high. 1.4 mm wide.

Etymology.-Named according to the Mahajanga Basin.

Types.-Holotype MB.Ga.1805. microfossil bed; paratype MB.Ga.1806, microfossil bed.

Other material examined.-Forty-four specimens from the microfossil bed (MB.Ga.1863).

Occurrence.-Albian, Mahajanga Basin. Madagascar.

Discussion.-The strongly opisthocyrt suture of the protoconch suggests the presence of a larval hook.

Family EUMETULIDAE Golikov and Starobogatov, 1975

Genus VATOPSIS Grndel, 1980

Type species.-Cerithium bimoniliferum Sandberger, 1858; Oligocene, Germany.

VATOPSIS? sp.

Figure 4.13

Description.-Protoconch turriculate, of four whorls, first three smooth, last with equally strong, sinuous collabral ribs and two spiral cords, height about 635 m, width about 345 m. One teleoconch whorl preserved, turriculate, weakly convex, ornament of three spiral cords and slightly oblique axial ribs. Incomplete shell 0.9 mm high, width 0.4 mm.

Material examined.-One specimen from the microfossil bed, MB.Ga.1808.

Occurrence.-Albian, Mahajanga Basin, Madagascar.

Discussion.-All hitherto described species of Vatopsis have spiral and collabral ornament on most of the larval shell. This kind of ornamentation is only present on the last whorl of the larval shell of Vatopsisl sp., while the first three whorls are smooth, as in Recent Cerithiopsis Forbes and Hanley, 1849. Because shape and ornamentation of the adult shells of Vatopsis and Cerithiopsis are very similar, Vatopsis? sp. can be interpreted as transitional between the two genera. Therewith it would also be transitional between the Eumetulidae and Cerithiopsidae H. and A. Adams, 1854.

Family NYSTIELLIDAE Clench and Turner, 1952

Genus OPALIOPSIS Thiele, 1928

Type species.-Opaliopsis elata Thiele, 1925; Recent, South Africa.

OPALIOPSIS FRANCISCAE (Collignon, 1949)

Figure 4.14-4.16

Scala (Confusiscala) Franciscae COLLIGNON, 1949, p. 29-30, pl. 5, figs. 1-3.

Scala (Confusiscala) Odilae COLLIGNON, 1949, p. 30-32, pl. 5, figs. 4, 5.

Description.-Protoconch turriculate, of six whorls with collabral, sicklelike ribs from suture to suture, larval hook only poorly developed: height about 1,180 m, width about 500 m. Teleoconch slender-turriculate. whorls convex, ribs varixlike. about 10 on the earliest whorls, increasing up to 16 on last whorls, crossed by about 10 line spiral lirations; last whorls develop a subsutural collar on some specimens; base with one or two spiral cords; aperture subcircular. Figured juvenile shell 3.0 mm high, largest adult shell 41.0 mm high and 19.0 mm wide.

Material examined.-Two specimens from the ammonite bed (MB.Ga.1810-11), 10 specimens from the microfossil bed (MB.Ga.1865). figured MB.Ga.1812.

Occurrence.-Albian, Mahajanga Basin, Madagascar.

Discussion.-Of the two available adult shells, the larger one could be identified as Scala (Conftisiscala) odilac. the smaller one as S. (C.) franciscae, considering the descriptions of Collignon (1949). However, the smaller specimen has 11 ribs on the first whorl and 13 on the last, the larger specimen has 14 ribs on the first whorl and 16 on the last. Additionally, the ribs of the larger specimen show a change in shape from straight on the early whorls to slightly sinuous on the last whorls, whereas those of the smaller specimen are all straight. It is thus likely that S. (C.) odilae represents only a later growth stage of S. (C.) franciscae. The juvenile specimens have 10 ribs on the earliest teleoconch whorls. All these specimens are here interpreted as belonging to the same species. As first reviser, 1 select Opaliopsis franciscae as the valid name for the species named both Scala franciscae and S. odilae by Collignon (1949). The species is placed in Opaliopsis rather than Confusiscala Boury, 1909, because Confusiscala has lamella-like ribs while those of S. (C.) fransiscae are rather varix like, as in Opaliopsis.

OPALIOPSIS aff. DUPINIANUM (d'Orbigny, 1842)

Figure 5.1-5.3

Cerithium dupinianum D'ORBIGNY, 1842, p. 354, pl. 227, figs. 4- 6.

Description.-Protoconch turriculate, of four whorls; embryonic part half a whorl, smooth, 140 m wide: larval shell with collabral, sicklelike ribs from suture to suture; transition to teleoconch with a strong larval hook: height about 630 m width about 350 m. Teleoconch slender turriculate, whorls convex, with about 12 sharp- edged axial ribs, live spiral cords, the first a little weaker than lower four, spiral and axial sculpture of almost equal strength, forming tubercles at their intersections: aperture slightly oval, columella without folds. Figured specimens 1.2 mm high (5.1, 5.2) and 2.0 mm high (5.3).

Material examined.-Seven specimens from the microfossil bed (MB.Ga.1864). figured specimens MB.Ga.1807 and 1844.

Occurrence.-Albian of the Mahajanga Basin, northwestern Madagascar.

Discussion.-The teleoconchs of the my specimens agree well with d'Orbigny's figures, however, the protoeonch of dOrbigny's species is unknown, and thus the Madagascan species concerned here is only tentatively considered conspecific with Opaliopsis dupinianwn. The axially ribbed, slender-turriculate protoeonch indicates that this species belongs to the nystiellid Opaliopsis. rather than Cerithium Bruguiere, 1789. where d'Orbigny had placed it.

Genus IPHITUS Jeffreys, 1883

Type species.-Iphitus tuheralus Jeffreys, 1883; Recent, Atlantic Ocean.

IPHITUS sp.

Figure 5.4, 5.5

Description.-Protoconch turriculate, at least three-and-a-half whorls, with 15-20 orthocline ribs per whorl, crossed by five to eight fine spiral lines; terminating in a larval hook with thickened outer lip, height at least 730 m, width about 450 m. Teleo\eonch with at least one-and-a-half convex whorls, about 20 axial ribs per whorl, crossed by eight spiral cords, the lower four covered by the succeeding whorl; aperture lenticular, eolumelia smooth. Incomplete specimen 2.4 mm high, width 1.4 mm.

FIGURE 5-Albian gastropods from northeastern Madagascar. 1-3, Opaliopsis aff. dupinianum (d'Orbigny, 1842); 1, juvenile shell showing transition from proto- to teleoconch, MB.Ga.1807, microfossil bed, height 1.2 mm, 40, 2, apical view on same specimen as in 1, showing the smooth embryonic shell, 200, 3, juvenile shell, MB.Ga.1844. microfossil bed, height 2.0 mm, 60. 4, 5, Iphitus sp., MB.Ga.1809, microfossil bed, 2.4 mm, 4, apertural view, 20, 5, close- up on the protoconch, 60. 6-8. Conjectura minuta n. sp.; 6n holotype, MB.Ga.1827, microfossil bed, diameter (1.8 mm, 70, 7, basal view on paratype, MB.Ga.1828, microfossil bed, diameter 0.8 mm, 70, 8, close-up on protoconch of holotype, 150. 9-11, Buvignieria benvaldi n sp.; 9, holotype, MB.Ga.1816, microfossil bed, height 1.2 mm, 60, 10, protoconch of paratype, MB.Ga.1817, microfossil bed, 90, 11, embryonic shell of the same specimen as 10, 300. 12-16, Latiala besairiei (Collignon, 1949); 12, specimen showing the anterior lobe of the outer lip, MB.Ga.1819. ammonite bed. height 22 mm, 2, 13, 14, adult shell showing the posterior extension of the outer lip, MB.Ga.1818, ammonite bed, height 29 mm, 2, 15, protoconch, transition to teleoconch at the onset of axial ornamentation, MB.Ga.1820, ammonite bed, 20, 16, embryonic shell, MB.Ga.1821, microfossil bed, 100.

Material examined.-One specimen from the microfossil bed, MB.Ga.1809.

Occurrence.-Albian, Mahajanga Basin, Madagascar.

Discussion.-Iphitus sp. from the upper Miocene in southeastern Spain (Barrier et al., 1991, pl. 4, figs. 4. 5) differs from the one described here by having fewer spirals on the early teleoconch whorls. A Recent species reported from 370 and 690 m depth in the Mediterranean also has fewer spirals on the early teleoconch whorls, has a shorter larval hook than the species described here, but shows fine spirals on the protoeonch (Taviani and Sabelli, 1982). I. tuberatus and I. cancellatus Dautzenberg and Fischer, 1896 from the northeast Atlantic (Bouchet and Warn, 1986) have oblique ribs in contrast to the orthocline ribs of Iphitus sp. described here. Although there is a large time gap of about 75 Ma between this species and the oldest hitherto known species of Iphitus, the upper Eocene I. whipplei (Ladd, 1970, emend. Bouchet and Warn, 1986), the Albian Iphitus sp. is so close in shape to the extant type species that there is little doubt of its placement. It is described in open nomenclature because the only available specimen has only one teleoconch whorl preserved.

Family VITRINELLIDAE Bush, 1897

Genus CONJECTURA Finlay, 1927

Type species.-Crossea glabellu Murdoch, 1905; Recent, New Zealand.

CONJECTURA MINUTA new species

Figure 5.6-5.8

Diagnosis.-Protoeonch of one-and-a-quarter whorls, smooth, whorls increasing in diameter rapidly; teleoconch globular, lowspired; umbilicus conical, deep; base and umbilical margin keeled; whorls subsulurally slightly constricted.

Description.-Protoeonch planispiral. whorls increasing in diameter rapidly, one-and-a-quarter whorls; diameter about 280 m; embryonic part 80 m wide, sculptured with a line granular pattern; larval shell with line, prosocyrt growth lines. Teleoconch gyrodilonn, of up to two whorls; whorls subsuturally constricted. bearing sculpture of growth lines only, basal margin angulated to keeled, with a corresponding notch in the outer lip; umbilicus narrow, conical, deep, bordered by a strong ridge; aperture roundish to lenticular. Holotype about 0.9 mm high, width 0.8 mm. apical angle 108.

Etymology.-This species is significantly smaller than those previously described.

Types.-Holotype MB.Ga.1827. microfossil bed; paratype MB.Ga.1828, microfossil bed.

Other material examined.-Twenty-five specimens from the microfossil bed (MB.Ga.1873).

Occurrence.-Albian, Mahajanga Basin, Madagascar.

Discussion.-Conjectura minuta is very similar to the extant type species of Conjectura. C. glabella, from which it differs by having a lower spire, a broader base, a smaller initial whorl of the protoconch. and being only about half the size. Conjectura was previously only known from Miocene to Recent of New Zealand (Powell, 1979): this new record extents its fossil range considerably.

Family RISSOIDAE Gray, 1847

Genus BUVIGNIERIA Cossmann, 1921

Type species.-Rissoa unicarina Buvignier, 1843; Late Jurassic (Oxfordian), France.

BUVIGNIERIA BERWALDI new species

Figure 5.9-5.11

Diagnosis.-Embryonic shell with six spiral cords; two larval whorls, with sculpture of short spiral and oblique ribs, forming rhombs over the central area of the whorls; no larval hook. Teleoconch fusiform, whorls convex, sculpture of equally strong spiral cords and axial ribs, aperture lenticular, basal slope smooth.

Description.-Protoconch broadly conical, two-and-a-half convex whorls: transition to teleoconch abrupt, with no larval hook; about 300 m high and about 500 m wide: embryonic part half a whorl, width 160 m, with six line spiral lines that disappear before transition to larval shell: first larval whorl with fine, subsutural ribs, second whorl with complex pattern of oblique ribs and spirals, forming rhombs over the central area of the whorl. Teleoconch fusiform, of three convex whorls, sculpture of about 24 narrowly spaced axial ribs per whorl, crossed by three to four spiral cords and numerous fine tubcrculute rows: aperture lenticular, with short basal spout, columella smooth. Holotype 1.2 mm high, width 0.7 mm.

Etymology.-Named for Lars Berwald, Selent, for his help organizing the field work.

Types.-Holotype MB.Ga.1816, microfossil bed; paratype MB.Ga.1817, microfossil bed.

Other material examined.-More than 200 specimens from the microfossil bed (MB.Ga.1867).

Occurrence.-Albian, Mahajanga Basin, Madagascar.

Discussion.-This species is placed within the Rissoidae because of its spiral sculpture on the embryonic shell, which is characteristic for this family (Warn, 1993. 1996a). Buvignieria bandeli Kaim, 2004 from the Valanginian of Poland is the oldest known species to show this character. B. berwaldi differs from previously described species of Buvignieria (including K. bandeli) by its zigzag, stairlike rhomboid pattern on the protoconch; the protoconchs of other Binignieria species are either smooth or show fine, spiral, or irregular striae (Grndel, 2003; Kaim, 2004).

Family APORRHAIIDAE Mrch, 1852

Genus LATIALA Sohl, 1960

Type species.-Anchura lobata Wade, 1926; Late Cretaceous (Maastrichtian), USA.

LATIALA BESAIRIEI (Collignon, 1949)

Figure 5.12-5.16

Anchura (Perissoptera) Besairiei COLLIGNON, 1949, p. 37, pl. 4, figs. 22-26.

Description.-Protoconch dome-shaped with flattened top, of four whorls; embryonic part half a whorl, 130 m wide, suture with larval shell well demarcated; first larval whorl almost planispiral, basal keel well developed; later whorls forming a conical shell, growth lines strongly sinuous, transition to teleoconch marked by the onset of axial ribs; height of protoconch 2.3 mm, width 2.0 mm. Teleoconch high-spired, of about eight convex whorls, with 24 thin, opisthocyrt to opisthocline ribs per whorl, crossed by 14 fine spirals; about two irregular varices per whorl; on the last two whorls the four subsutural spiral cords become stronger, those on the periphery weaker; axial ribs stronger and more widely spaced on last half- whorl, their crests forming a ridge that continues onto the wing; wing almost triangular, outer margin pointed, reinforced, posterior extension attached to penultimate whorl; aperture elongate lenticular, inner lip smooth. Figured adult shells 29.0 mm high, width 22.0 mm (Fig. 5.13, 5.14), and 22.0 mm high, width 16.0 mm (Fig. 5.12).

Material examined.-More than 200 specimens from the ammonite bed (MB.Ga.1868), figured MB.Ga.1818-19; 75 specimens (larval shells only) from the microfossil bed (MB.Ga.1869), figured MB.Ga.1820-21.

Occurrence.-Albian, Mahajanga Basin, Madagascar.

Discussion.-A similar species of Aptian/Albian age is Latiala hayamii from Japan. That species differs from Latiala besairiei by having fewer axial ribs per whorl. Both species have a ridge that continues from the crests of the ribs on the last whorl onto the wing. With that character, these two species are intermediate between Latiala and Graciliala Sohl, 1960. Graciliala differs from Latiala by having a keel on the outer side of the wing, and by having some minor digitations that frill the lower margin of the wing (Sohl, 1960; Kiel and Bandel, 2002). The latter character is absent from L. hayamii and L. besairiei. Sohl (1960) and Kiel and Bandel (2002) assumed that Graciliala is derived from Drepanocheilus Meek, 1864. However, considering these intermediate species, Graciliala and Latiala may be considered sister taxa, derived from a common ancestor.

Genus TESSAROLAX Gabb, 1864

Type species.-Aporrhais (Tessarolax) distorta Gabb, 1864; Late Cretaceous (Campanian), USA.

Discussion.-While Cossmann (1904) and Wenz (1938-1944) considered Ceratosiphon Gill, 1870 a junior synonym of Tessarolax, Kase and Maeda (1980) distinguished the two genera due to the prominent axial projection opposite the aperture in Tessarolax, and the branching siphonal spine in Ceratosiphon. However, in their list of species included in Ceratosiphon, they included T. retusa, a species that lacks a branching siphonal spine. Although the type species of Tessarolax is only poorly preserved (see Stewart, 1927, pl. 23, fig. 4), the treatment of Cossmann (1904) and Wenz (1938-1944) is followed here.

TESSAROLAX RETUSA (Sowerby, 1836)

Figure 6.1-6.3

Rostellaria retusa SOWERBY, 1836, p. 344, pl. 18, fig. 22.

Aporrhais retusa (SOWERBY, 1836). GARDNER, 1875, p. 52, pl. 3, figs. 1-6.

Aporrhaisbicarinata DESHAYES, 1842. WOLLEMANN, 1900, p. 172, pl. 8, fig. 10.

Description.-Protoconch conical, smooth; growth lines sinuous; whorls convex; larval hook present, transition to teleoconch marked by onset of axial and spiral sculpture; width about 1.3 mm. Teleoconch biconical, apical angle about 50, of at least fourand-a- half whorls; whorls convex, with median keel, four minor spiral cords above and below median keel, basal keel covered by succeeding whorls; growth lines strongly opisthocyrt; outer lip with three projections, first projection attached to spire, extending up to the apex, with corresponding groove on apertural face; second projection extends laterally from median keel, pointing slightly posteriorly; third projection extends from basal keel, pointing slightly anteriorly; rostrum long, thin, after a sharp bent just below the aperture gently curving in opposite direction as the second and third projections; basal margin with six minor spiral cords; inner lip thick. Figured adult shell 20.0 mm high, width 23.0 mm.

Material examined.-Three specimens from the ammonite bed (MB.Ga.1870), figured MB.Ga.1822-23.

Occurrence.-Albian, Mahajanga Basin, Madagascar.

Discussion.-Gardner (1875) described an apical angle of 37.5 for his specimens of Tessarolax retusa. From his figures, however, apical angles from 40 to 65 can be measured. Also the number of minor spirals is quite variable in the English specimens investigated by Gardner (1875), ranging from two to twelve. The specimens described here fall within this variability and provide the first record of this species from outside Europe. Gardner (1875) provided an extensive synonymy of this species.

Family UNCERTAIN

Genus MAHAJANGINA new genus

Type species.-Mahajangina weitschati n. sp., by monotypy; Early Cretaceous (Albian), Madagascar.

Diagnosis.-Larval shell (when present) conical, bicarinate, with tuberculate microsculpture; teleoconch conical-trochiform, whorls angular, with spines at periphery.

Etymology.-Named after to the Mahajanga Basin.

Occurrence.-Albian, Mahajanga Basin, Madagascar.

Discussion.-Spines on the earliest teleoconch whorls are quite unusual among modern caenogastropods. They occur in some Xenophoridae Philippi, 1853, but xenophorid shells differ from the one described here by their large, smooth, low-trochiform to almost planispirally coiled protoconch (Bandel, 1993). The small, conical, and bicarinate protoconch of Mahajangina weitschati resembles that of certain Cerithiidae Fleming, 1822, Planaxidae Gray, 1850, Potamididae H. and A. Adams, 1854, and Procerithiidae, but members of these families usually have high-spired to turriculate teleoconchs with reticulate to spiral sculpture in contrast to the trochiform, spiny teleoconch of Mahajangina (Houbrick, 1987, 1991, 1992). Protoconchs similar to that of Mahajangina are also found among the Pickworthiidae Iredale, 1917 (Kase, 1999), but pickworthiids are usually lower spired. As there is only one incomplete (aperture missing) specimen of Mahajangina available, a more precise classification must await betterpreserved material.

MAHAJANGINA WEITSCHATI new species

Figure 6.4-6.7

Diagnosis.-As for genus, protoconch with four whorls, three rows of fine tubercles below lower keel; teleoconch with about 11 spines per whorl.

Description.-Protoconch conical, of four whorls, about 400 m high and wide, terminating in a larval hook; embryonic part half a whorl, about 100 m wide; larval shell bicarinate, keels with fine, oblique riblets, three rows of fine tubercles between lower keel and suture. Teleoconch of one-and-a-half angular whorls, row of spines on the lower half of the whorls; aperture circular. Holotype 1.1 mm high, width 1.0 mm.

Etymology.-Named for Wolfgang Weitschat, Hamburg, who drew my attention to gastropods trapped in the living chambers of ammonites from the Mahajanga Basin.

FIGURE 6-Albian gastropods from northeastern Madagascar. 1-3, Tessarolax retusa (Sowerby, 1836); 1, abapertural view. MB.Ga.1822, ammonite bed, height 20 mm, 2.5, 2, juvenile specimen with last whorl of protoconch preserved, MB.Ga.1823, ammonite bed, 20, 3, apertural view of the same specimen as 1. 4-7, Mahajangina weitschati n. gen. and sp., holotype, MB.Ga.1801. microfossil bed; 4, close-up on protoconch sculpture, 300, 5-7, three views of the holotype, height 1.1 mm, 45. 8-11. Emomope crassilabrum n. sp.; 8, holotype, MB.Ga.1813, microfossil bed, height 2.1 mm, 30, 9, juvenile shell with protoconch, MB.Ga.1815, microfossil bed, 150, 10, embryonic shell, MB.Ga.1814. microfossil bed, 400; 11, apical view on same specimen as 10, showing the thickened apertural margin, 30, 12-15, Paladmete? rasoarinoroue n. sp.; 12, 13, holotype, MB.Ga.1824, microfossil bed, height 17 mm, 3, 14, 15, paratype, MB.Ga.1825, microfossil bed, juvenile specimen; 14, apical view showing protoconch, transition to teleoconch at the onset of axial sculpture, 50, 15, close-up on embryonic shell showing tine tubercles, 100.

Type.-Holotype MB.Ga.1801, from the ammonite bed (only specimen).

Occurrence.-Albian, Mahajanga Basin, Madagascar.

Genus ENTOMOPE Cossmann, 1888

Type species.-Litiopa klipsteini Cossmann, 1882, Middle Eocene (Lutetian), France.

ENTOMOPE CRASSILABRUM new species

Figure 6.8-6.11

Diagnosis.-Embryonic shell with fine polygonal pits and wrinkles; two larval whorls, whorls sculptured by very fine tubercles and a fine basal cord, no larval hook. Teleoconch elongate, two-and-a- half convex whorls, with sculpture of seven to ten rows of spiral pits; no umbilicus; outer lip with a varixlike thickening.

Description.-Protoconch conical to dome-shaped, of two-anda-half whorls, about 320 m high, about 435 m wide; embryonic part about 115 m wide, with very fine polygonal pits and wrinkles, suture with larval shell weakly sinuous; larval whorls convex, with sculpture of very fine tubercles and a fine basal cord, growth lines sinuous; suture with adult shell weakly sinuous. Teleoconch Hydrobia-shaped, two-and-a-half weakly convex whorls, with sculpture of seven to ten spiral rows of pits; columella thick, slightly bent towards the outer lip; aperture lenticular, posterior end weakly pointed, anterior end weakly notched, inner lip strongly callused, outer lip thickened, peristome uninterrupted, smooth. Holotype 2.1 mm high, width 1.2 mm.

Etymology.-For its thickened outer lip.

Types.-Holotype MB.Ga.1813, paratypes MB.Ga.1814-15.

Other material examined.-Eighty specimens from the microfossil bed (MB.Ga.1866).

Occurrence.-Albian, Mahajanga Basin, Madagascar.

Discussion.-The multiwhorled protoconch of Entomope crassilabrum, with a clear distinction from the teleoconch, indicates planktotrophic development. Although the larval shell is clearly demarcated from the teleoconch along a sinuous margin, the absence of a larval hook is noteworthy. Entomope crassilabrum differs from Entomope ponderi (Dockery, 1993, p. 56, pl. 10, figs. 4, 5; pl. 41, figs. 1, 2) from the Coon Creek Campanian of Tennessee, USA, by lacking an umbilicus, and by its thickened outer lip.

Entomope was initially placed among the Lacuninae (Cossmann, 1888; Wenz, 1938-1944), but Dockery (1993) transferred the genus to the Iravadiidae Thiele, 1928 referring to its similarity to the iravadiid genus Nozeba Iredale, 1915. There are three objections to the placement of Entomope crassilabrum among Nozeba or the Iravadiidae: first, none of the iravadiids described by Ponder (1984) has the fine polygonal pattern on the embryonic shell seen in E. crassilabrum; second, all iravadiids have a protoconch with a flattened apex, with the initial part imbedded in the succeeding whorls (Ponder, 1984). The protoconch of E. crassilabrum is broadly conical and the initial part is not embedded. Also the Campanian E. ponderi has a broadly conical protoconch; third, Nozeba does not have a varixlike apertural thickening (Ponder, 1984), like the species described here.

However, there are also objections to a placement of Entomope among the littorinid subfamily Lacuninae. While larval shells of extant littorinids are conical to pointed-conical with strong spiral ornament (Bandel and Kadolsky, 1982; Reid, 1986), most extant lacunines have no planktotrophic development, except for two species of the Australian genus Bembicium Philippi, 1846 (Reid, 1988). However, in these species the larval phase is only short and the protoconchs consist of one-and-a-half whorls at most, are low and dome-shaped, and are smooth (Reid, 1988, p. 97, figs. 17d, 22d). Thus both protoconch types differ from that of Entomope. Also the shape of the teleoconch of Entomope is not very conclusive for taxonomic purposes. Slender shells with incised spirals are known from littorinids, iravadiids, and rissoids. In conclusion, Entomope can safely been placed among the Caenogastropoda based on protoconch characters, and within this group it most probably belongs in the Littorinimorpha Golikov and Starobogatov, 1975, based on the shape of its teleoconch. Its position within the Littorinimorpha, however, is still uncertain.

Genus PALADMETE Gardner, 1916

Type species.-Trichotropis cancellaria Conrad, 1858; Late Cretaceous (Maastrichtian), USA.

Discussion.-The taxonomic position of Paladmete has always been a matter of doubt. Its type species bears the ambiguous name Trichotropis cancellaria and, nomen est omen, it has most commonly been placed either in the Cancellariidae (Gardner, 1916; Stephenson, 1941; Sohl, 1964) or in the Trichotropidae (Cossmann, 1925; Wenz, 1938-1944). More recently, Bandel and Dockery (in press) placed it in the Tonnoidea. Paladmete? rasoarinoroae n. sp. resembles Paladmete in characters of the teleoconch, but differs slightly in the morphology of its protoconch: it is comparably small, comprises only one-and-a-half whorls, and is smooth, while the protoconch of Paladmete s.s. is apically flattened and comprises two to three whorls (Wade, 1926; Ste\phenson, 1941, 1952; Sohl, 1964). Protoconchs similar to that of Paladmete? rasoarinoroae are described from certain littorinids (see Reid, 1996). Littorinids also have teleoconchs similar to that of Paladmete (see Reid, 1996), but usually have spiral sculpture rather than axial ribs. In addition, tubercles on the embryonic shell similar to those seen on Paladmete? rasoarinoroae are today found among many Neogastropoda and also in the Naticidae, but not among littorinids (Bandel, 1975). Paladmete? rasoarinoroae therefore most likely belongs to the 'higher' Caenogastropoda.

PALADMETE? RASOARINOROAE new species

Figure 6.12-6.15

Diagnosis.-Protoconch globular, of one-and-a-half whorls, smooth; embryonic shell about 200 m wide, with fine, widely spaced tubercles; teleoconch littoriniform, of five convex whorls, with prosocline axial ribs and five major spiral cords; occasional varices, umbilical slit present.

Description.-Protoconch low, globular, one-and-a-half whorls, transition to teleoconch indistinct, about 500 m wide; embryonic part about 210 m wide, with fine, widely spaced tubercles. Teleoconch littoriniform, with five convex whorls; axial ribs fine, slightly oblique and prosocline, continuous into umbilical slit; five major and a few minor spiral cords on lower half of whorl; low, narrow varices situated irregularly on all whorls; aperture rounded lenticular, columella smooth. Holotype 17.0 mm high, width 13.0 mm.

Etymology.-Named for Madame Rasoarinoro, Antananarivo, who made the field trip to the fossil locality possible.

Types.-Holotype MB.Ga. 1824, microfossil bed; paratype MB.Ga.1825, microfossil bed.

Other material examined.-Eleven specimens from the ammonite bed (MB.Ga.1871) and six specimens from the microfossil bed (MB.Ga.1872).

Occurrence.-Albian, Mahajanga Basin, Madagascar.

Discussion.-A similar species from the German "Neokomian" is Fusus brunsvicensis Wollemann, 1900 (p. 174, pl. 8, figs. 11, 12). That species differs from the one described here by its more prominent axial ribs; its protoconch is unknown. Also of similar general shape and with similar varices, but without spiral sculpture is Natica ervyna d'Orbigny, 1842, as figured by Wollemann (1906, p. 287, pl. 9, figs. 4, 5) from the Aptian/Albian of Algermissen, Germany. D'Orbigny's (1842, p. 159, pi. 173, tig. 7) original figure of Natica ervyna does not show varices and lacks an umbilicus, and might not be congeneric.

Subclass HKTHROBRANCHIA Gray, 1840

Family CORNIROSTRIDAK Ponder, 1991

Genus TOMURA Pilsbry and McGinty, 1946

Type species.-Vitrinella (Tomura) bicaudata Pilsbry and McGinty, 1946; Recent, Florida.

TOMURA AMBATOLAFIENSIS new species

Figure 7.1-7.5

Diagnosis.-Protoconch small for the genus, of one-and-a-quarter whorls, embryonic part sunken, with fine polygonal pattern.

Description.-Protoconch almost plunispiral, of one-and-a-quarter whorls, about 200 m; wide: embryonic part of halt a whorl, slightly sunken, 100 m, wide, first half sculptured with fine, polygonal pits; larval shell smooth. Teleoconch skeneiform, of about one-and- a-half convex whorls, smooth except for growth lines; aperture subcircular, umbilicus narrow. Holotype 0.5 mm high, width 0.7 mm, apical angle 140.

Etymology.-Named lor the village of Ambatolatia, near the type locality.

Type.-Holotype MB.Ga. 1826, microfossil bed.

Occurrence.-Albian, Mahajanga Basin, Madagascar.

Discussion.-The assignment of fossil species to the Cornirostridae with their rather featureless shells is problematic (Bieler et al., 1998). However, some conclusions can be drawn from the present data. Bieler et al. (1998, table 1) summarized characters of extant cornirostrids. They showed that Tomura includes shells with and without a keeled umbilicus, while in Cornirostra Ponder, 1991 the umbilicus is always unkeeled. Schroder ( 1995) and Bandel (1996) considered the Triassic to Lower Cretaceous Bandellina Schrder, 1995 to belong to the Cornirostridae. Its shells generally resemble those of extant cornirostrids but differ in protoconch size. In extant cornirostrids with planktotrophic ontogeny, protoconch sizes range from 108 to 217 m (Bieler et al., 1998, table 1), whereas in fossil Bamlellina the protoconch measures about 280 m (Schroder, 1995; Bandel, 1996). The species described here has a keeled umbilicus and its protoconch has a diameter of 200 m. It is therefore placed in Tomura. and represents the oldest member of this genus.

Family MATHILDIDAE DaIl, 1889

Discussion.-Mathildids show a broad range of shell shapes from conical to very slender turriculate, and their sculptural elements include spiral ridges, cords, and threads, as well as axial ribs and riblets of various strength. Sculpture is subject to profound ontogenetic changes (i.e., Gvmnolhilda pagodoidea n. sp., Fig. 8.1, 8.2). The genera among the mathildids have so far only been classified according to shell shape, and these classifications have never been verified by comparison to anatomical, morphological, or molecular data. The classification here follows largely that of Kaim (2004), and brief annotations are made regarding the generic characteristics.

Genus CARINATHILDA Griindel, 1997

Type species.-Carinathilda carinata Grundel, 1997; Mid-Jurassic (Bathonian), Poland.

Discussion.-Carinaihilda includes high-spired mathildids with two major initial spiral ridges, fine axial riblets, and fine spiral threads. It apparently is common praxis to disregard the

Source: Journal of Paleontology

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