154 THE GASTROPODA 



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

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

 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- 

 culum 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, 

 Ferussac. Nasxopsis, Smith. Bythoceras, Moore ; from Lake Tanganyika. 

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

 turriculated, with carinated whorls, the carinae ttiberculated 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. Potamides, Brong- 

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

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

 Dunker and Metzger. Cerithiopsis, 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 ; 



