CLASS IV 



GASTKOPODA 



537 



Silnrian to Trias ; paiticiilarly 



deep ; aperture higlier tlian wide, with shallow canal. 

 abundaiit in tlie Carboniferoiis. 



Zygopleura Koken. Like the last, but whorls with sharp, sliglitly curved 

 transverse ribs, or transverse nodose keel. Devonian to Lower Cretaceoiis. 



Bourgetia Deshayes {Pithodea de Kon.). Lai-ge, 

 elongate-oval to turreted, with large, inflated body 

 whorl. Snrface marked with spiral Striae or furrows. 

 Carboniferous and Upper Jura. 



Pseudomelania Pictet {Chemnitzia p.p. d'Orbigny) 

 (Fig. 913). Turreted, with 

 numerous, ahnost flat whorls, 

 and slightly impressed sutures. 

 Snrface smooth, or marked by 

 fine growth-lines ; aperture 

 rounded anterioiiy, or with 

 faint canal. Unibilicus want- 

 ing; rarely an umbilical fissure 

 present. Very abundant in the 

 Trias and Jura, less so in 

 Cretaceous and Eocene ; prob- 

 ably present also in the Car- 

 boniferous. 



Siibgenera : Oonia, Microschiza 

 Geram. ; Hypsipleura, Anoptychia 

 Koken. Trias and Jura. Coe- 

 lostylina, Eiistylus, Spirostylus 

 Kittl. Trias. Bayania Munier- 

 Chalm. (Fig. 914). Eocene. 



Fio. 912. 

 Macroclieilus arculatus 

 (Schloth.). Middle De- 

 vonian ; Paffrath, near 

 Cologne. 



Fio. 913. 



Pseudomelania 

 heddingtonensis 

 (Sowb.). Oxford- 

 ian ; France. Bands 

 of original colora- 

 tion still showing. 



Fig. 914. 



Pseudomelania 

 (Bayania) lactea 

 Lam. sp. Cal- 

 caire Grossier ; 

 Grignon, near 

 Paris. 



Pustularia Koken, non Swains. Turreted, with groove-like sutures. WhorLs 

 flat, with three or more spiral rows of nodes. Trias. 



Gatosira Koken. Whorls flat, with transverse ridges. Aperture canaliculate ; 



base with spiral grooves. Trias and Jura. 



Biastoma Desh. (Fig. 915). Like the last, 

 but aperture separated from the body whorl. 

 Whorls with transverse folds and spiral Striae. 

 Cretaceous to Recent. 



Mathilda Semper {Promathilda Andreae). 

 Turreted ; whorls transversely and spirally 

 striated or ribbed. Aperture with canaL Proto- 

 conch heterostrophic. Jura to Recent. 



Keilostoma Desh. {Paryphostoma Bayan) (Fig. 

 916). Turreted, spirally striated. Outer lip 

 with externally thickened margin. Eocene. 



Turbonilla Risso {Chemnitzia p.p. d'Orb.) (Fig. 

 917). Small, turreted, with heterostrophic proto- 

 conch. Whorls transversely ribbed or smooth. 

 Inner lip straight, or occasionally with folds. 

 Tertiary and Recent. 



Odostomia Fleming (Fig. 918); Pyramidella 



Lamarck (Fig. 919). Cretaceous to Recent. 



Tertiary and Recent. Palaeoniso Gemm. Trias 



Fig. 915. 



Diastema costcllata 

 (Lam.). Calcaire 

 Grossior ; Daniery, 

 near Bpernay. 



Syrnola Adams 

 and Jura. 



The genera 



Fig. 916. 



Keilostoma turricula 

 Brug. sp, (Melania 

 margiimta Lamarck). 

 Calcaire Grossier ; 

 Grignon, near Paris. 



Eidimella Fischer. 



Suhulites Conrad (? Pohjphemopsis Portlock), from the Cambrian t^ 



