154 THE GASTROPODA 



divided into two sections by a transverse furrow ; penis without an 

 appendage. Bithynella, Moquin - Tandon. Lithoglyphus, Miihlfeldt ; 

 shell globular with short spire. Spekia, Crosse ; viviparous ; from Lake 

 Tanganyika. Tanganyicia, Crosse (Fig. 78). Limnotrochus, Smith ; 

 from Lake Tanganyika. Chytra, Moore. Littorinida, Eydoux and 

 Souleyet Bithynia, Gray ; shell conical with an oval aperture ; oper- 

 culuni calcareous, concentric ; habitat fluviatile ; British. Stenothyra, 

 Benson ; aperture rounded and contracted ; operculum calcareous, spiral. 

 FAMILY 21. MELANIIDAE, Gray. Shell spiral, the spire somewhat elon- 

 gated ; operculum horny ; foot and snout short ; mantle border fringed ; 

 viviparous (Fig. 109); fluviatile. Genera Melania, Lamarck ; shell turri- 

 culated ; aperture rounded and enlarged anteriorly. Faunus, Montfort ; 

 spire very long ; aperture of shell notched anteriorly. Paludomus, 

 Swainson ; shell short, thick, with rounded aperture. Melanopsis, 

 Fe'russac. Nastopsis, Smith. Bythoceras, Moore ; from Lake Tanganyika. 

 FAMILY 22. TYPHOBIIDAE, Moore. Foot wide ; tentacles elongate ; shell 

 turriculated, with carinated whorls, the carinae tul>erculated or spiny. 

 Genera Ty phobia, Smith. Bathanalia, Moore ; from Lake Tanganyika. 

 FAMILY 23. PLEUROCERIDAE, Fischer. Like the Melaniidae, but the 

 border of the mantle is not fringed and the reproduction is oviparous. 

 Genera Pleurocera, Rafinesque ; shell elongated ; the aperture canaliculated 

 anteriorly. Anculotus, Say ; shell short, globular ; the aperture rounded 

 anteriorly. FAMILY 24. PSEUDOMELANIIDAE, Fischer. An exclusively 

 fossil family ; shell turriculated, with prominent spire and elongated oval 

 aperture. Genera Pseudomelania, Pictet and Campiche ; Secondary and 

 Tertiary. Loxonema, Phillips ; Palaeozoic. Macrochilus, Phillips ; 

 Devonian to Trias. FAMILY 25. SUBULITIDAE, Fischer. An exclusively 

 fossil family ; shell turriculated with a narrow aperture, elongated and 

 canaliculated anteriorly. Genera Subulites, Conrad ; Cambrian to Car- 

 boniferous. Fusispira, Hall ; Ordovician. Euchrysalis, Laube ; Trias. 

 FAMILY 26. NERINEIDAE, Zittel. An exclusively fossil family ; shell with 

 numerous whorls, with multiple folds in the lumen of the whorls. 

 Genera Nerinea, Defrance ; Jurassic and Cretaceous. Aptyxiella, Fischer ; 

 Trias and Jurassic. Ptygmatis, Sharpe ; Jurassic and Cretaceous. FAMILY 

 27. CERITHIIDAE, Fleming. Shell with elongated spire and numerous 

 tuberculated whorls ; aperture canaliculated anteriorly ; snout long ; 

 pallial siphon short. Genera Cerithium, Adanson ; aperture oval ; 

 operculum oval, with submarginal nucleus. Bittium, Gray ; operculum 

 circular, with central nucleus ; siphon rudimentary. Potamiiles, Brong- 

 niart ; eyes situated above the bases of the tentacles ; ctenidium rudi- 

 mentary ; brackish water. Triforis, Deshayes ; shell sinistral. Laeocochlis, 

 Dunker and Metzger. Cerithinpsis, Forbes and Hanley. FAMILY 28. 

 MODULIDAE, Fischer. This family differs from the Cerithiidae in having 

 a shell with a short spire, without a siphon ; the eyes are placed midway 

 up the tentacles. Genus Modulus, Gray. FAMILY 29. VERMETIDAE, 

 d'Orbigny. The animal is fixed by the shell, the last whorls of which are not 

 in contact with one another ; foot small, discoidal, with two anterior pedal 

 tentacles, one on each side of the supra-pedal gland. Genera Vermetus, 

 Adanson ; shell without a notch on the exterior border of the aperture ; 



