154 THE GASTROPODA 
divided into two sections by a transverse furrow; penis without an 
appendage.  ithynella, Moquin-Tandon. Lithoglyphus, Miihlfeldt ; 
shell globular with short spire. Spekia, Crosse ; viviparous; from Lake 
Tanganyika. ‘anganyicia, 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. 
Famity 21. Mrevanupak, 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. Haunus, Montfort ; 
spire very long; aperture of shell notched anteriorly. Paludomus, 
Swainson; shell short, thick, with rounded aperture. Melanopsis, 
Férussac. Nassopsis, Smith. Bythoceras, Moore ; from Lake Tanganyika. 
Faminy 22, TypHostipA£, Moore. Foot wide; tentacles elongate ; shell 
turriculated, with carinated whorls, the carinae tuberculated or spiny. 
Genera—Typhobia, Smith. Bathanalia, Moore; from Lake Tanganyika. 
Famity 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. Faminy 24. PSEUDOMELANIIDAE, Fischer. An exclusively 
fossil family ; shell turriculated, with prominent spire and elongated oval 
aperture. Genera—Pseudomelania, Pictet and Campiche ; Secondary and 
Tertiary. Loxvonema, Phillips; Palaeozoic. Macrochilus, Phillips ; 
Devonian to Trias. Faminy 25. SuBuLitmasg, 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. Huchrysalis, 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—Cerithiwm, Adanson ; aperture oval ; 
operculum oval, with submarginal nucleus. Bittiwm, Gray ; operculum 
circular, with central nucleus; siphon rudimentary. Potamides, Brong- 
niart ; eyes situated above the bases of the tentacles; ctenidium rudi- 
mentary ; brackish water. | T'riforis, Deshayes ; shell sinistral. Laeocochlis, 
Dunker and Metzger. Cerithiopsis, Forbes and Hanley. Famity 28, 
Mopvipa®, 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. Famity 29. VERMETIDAE, 
@VOrbigny. 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 ; 
