150 THE GASTROPODA 
tertentacular lobes absent. Genus—Delphinula, Lamarck ; with five pairs 
of epipodial tentacles. Famity 11. Liormpan, Gray. Shell globular ; 
margin of aperture thickened ; operculum horny, with a caleareous 
layer. Genus—Liotia, Gray. Faminty 12. CycLostREMATIDAE, Fischer. 
Shell flattened, umbilicated, not nacreous; foot truncated anteriorly 
and with the two angles prolonged into tentacles. Genera—Cyclostrema, 
Marryat (Fam. 50), Tetnostoma, Adams. Famity 13. TROCHONE- 
MATIDAE, Zittel. Exclusively fossil, from Cambrian to Cretaceous ; shell 
spiral and nacreous internally ; whorls without keels; aperture rounded. 
Genera—Tvrochonema, Salter ; from the Cambrian and Silurian. Hunema, 
Salter ; from the Ordovician to the Devonian. Amberleya, Morris and 
Lycett ; from the Trias to the Cretaceous. Oncospira, Zittel ; Jurassic. 
Famity 14. Turpintnan, Gray. Visceral mass and shell spirally coiled ; 
epipodial tentacles present; eyes closed; operculum calcareous and 
thick. Genera— Turbo, Linnaeus; shell globular, thick, with short 
spire. Astralium, Link.  Mélleria, Jeffreys; shell thin, umbilicated, 
with very short spire. Cyclonema, Hall. Famity 15. PHASIANELLIDAE, 
Troschel. Shell not nacreous, without umbilicus, with prominent spire 
and polished surface. Genus— Phasianellu, Lamarck. Faminy 16. 
UmpontiIDAb, Adams. Shell flattened, not umbilicated, generally smooth, 
without a nacreous layer ; operculum horny. Genera—Umbonium, Link. 
Isanda, Adams. Faminty 17. NeriropsiDAg, Fischer. Shell semiglobular, 
with short spire ; operculum calcareous, not spiral. Genera—Neritopsis, 
Grateloup. Naticopsis, MacCoy ; from the Devonian to the Trias. Faminy 
18. Macturitipan, Fischer. Shell discoid, deeply umbilicated, with 
few whorls ; operculum spiral, thick. Genus—Maclurites, Lesueur ; from 
Cambrian and Silurian. Famity 19. NERITIDAE, 
Lamarck. Shell with very low spire; without um- 
bilicus and without a nacreous layer ; internal partitions 
frequently absorbed ; operculum calcareous, provided 
with an apophysis; epipodium slightly developed, 
without tentacles; a single ctenidium; a cephalic 
penis present. Genera— Nerita, Adanson ; marine. 
Neritina, Lamarck ; freshwater ; British. Nerztodomus, 
Morris and Lycett; Jurassic. Detanira, Stoliczka ; 
Cretaceous. Septaria, Férussac ; shell boat - shaped, 
with a large aperture and symmetrical muscular im- 
pressions. Pzleolus, Sowerby ; from the Jurassic and 
Cretaceous. Faminy 20. TiTiscANIIDAE, Bergh. With- 
out shell and operculum, but with a pallial cavity and 
a ctenidium. Genus—Titiscania, Bergh (Fig. 131) ; 
these uinabina: from the Pacific Ocean. Famity 21. HELIcINIDAR, 
dorsalaspect. I,eye; Pfeiffer. No ctenidium, but a pulmonary cavity 
He aos allied present; epipodium without tentacles; heart with a 
Pacey gill. single auricle, and not traversed by the rectum; no 
inandible ; operculum without apophyses. Genera— 
Helicina, Lamarck. FEutrochatella, Fischer. Stoastoma, Adams. Bourcteria, 
Pfeiffer, Faminy 22. Hyprocentpar, Fischer. No ctenidium, but a 
pulmonary cavity present; foot obtuse ; operculum calcareous, with an 
Fig. 131. 
