150 



THE GASTROPODA 



tertentacular lobes absent. Genus Delphinula, Lamarck ; with five pairs 

 of epipodial tentacles. FAMILY 11. LIOTIIDAE, Gray. Shell globular; 

 margin of aperture thickened ; operculum horny, with a calcareous 

 layer. Genus Liotia, Gray. FAMILY 12. CYCLOSTREMATIDAE, Fischer. 

 Shell flattened, umbilicated, not nacreous ; foot truncated anteriorly 

 and with the two angles prolonged into tentacles. Genera Cyclostrema, 

 Marryat (Fam. 50). Teinostoma, Adams. FAMILY 13. TROCHONE- 

 MATIDAE, Zittel. Exclusively fossil, from Cambrian to Cretaceous ; shell 

 spiral and nacreous internally ; whorls without keels ; aperture rounded. 

 Genera Trochonema, Salter ; from the Cambrian and Silurian. Eunema, 

 Salter ; from the Ordovician to the Devonian. Amberleya, Morris and 

 Lycett ; from the Trias to the Cretaceous. Oncospira, Zittel ; Jurassic. 

 FAMILY 14. TURBINIDAE, 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. Molleria, Jeffreys ; shell thin, umbilicated, 

 with very short spire. Cyclonema, Hall. FAMILY 15. PHASIANELLIDAE, 

 Troschel. Shell not nacreous, without umbilicus, with prominent spire 

 and polished surface. Genus Phasianella, Lamarck. FAMILY 16. 

 UMBONIIDAE, Adams. Shell flattened, not umbilicated, generally smooth, 

 without a nacreous layer ; operculum horny. Genera Umbonium, Link. 

 Isanda, Adams. FAMILY 17. NERITOPSIDAE, Fischer. Shell semiglobular, 

 with short spire ; operculum calcareous, not spiral. Genera Neritopsis, 

 Grateloup. Naticopsis, MacCoy ; from the Devonian to the Trias. FAMILY 

 18. MACLURITIDAE, Fischer. Shell discoid, deeply umbilicated, with 

 few whorls ; operculum spiral, thick. Genus Maclurites, Lesueur ; from 

 Cambrian and Silurian. FAMILY 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. Neritodomus, 

 Morris and Lycett ; Jurassic. Deianira, Stoliczka ; 

 Cretaceous. Septaria, Ferussac ; shell boat - shaped, 

 with a large aperture and symmetrical muscular im- 

 pressions. Pileolus, Sowerby ; from the Jurassic and 

 Cretaceous. FAMILY 20. TITISCANIIDAE, Bergh. With- 

 out shell and operculum, but with a pallial cavity and 

 a ctenidium. Genus Titiscania, Bergh (Fig. 131) ; 

 from the Pacific Ocean. FAMILY 21. HELICINIDAE, 

 Pfeiffer. No ctenidium, but a pulmonary cavity 

 of the pa/iiai present ; epipodium without tentacles ; heart with a 

 cavity; iv, gill, single auricle, and not traversed by the rectum; no 

 mandible ; operculum without apophyses. Genera 

 Helicina, Lamarck. Eutrocliatella, Fischer. Stoastoma, Adams. Bourcieria, 

 Pfeiffer. FAMILY 22. HYDROCENIDAE, Fischer. No ctenidium, but a 

 pulmonary cavity present ; foot obtuse ; operculum calcareous, with an 



FIG. 131. 



Titiscania limaeina, 

 dorsal aspect. I, eye ; 

 II, tentacle 

 opening 



