7 8 4 



COMPENDIUM OF GENERIC DISTINCTIONS. 



Genus. CYMBA. Nucleus large and globular, whorls few. 

 Rest like Voluta. Warm seas. 



Genus. MARGINELLA. Spire very short ; aperture trun- 

 cated in front; outer lip truncated when adult; columella 

 plaited. Warm seas. 



Family. CYPRvEID^E. Shell convoluted and enamelled. 

 Spire not visible ; aperture narrow, with a channel at each 

 end. Outer lip thickened. 



Genus. CYPR^EA. Shell swollen ; canals short ; outer lip 

 ridged. Most seas. 



Genus. OVULUM. Inner lip smooth. Rest like Cypraea. 

 Many seas. 



Section. HOLOSTOMATA (SEA SNAILS). Shell 

 spiral ; edge of aperture entire. Animal with gills like combs 

 or feathers set across back on to neck. No siphon. Opercu- 

 lum hard and shelly on exterior. 



Family. NATICID^. Shell globular ; whorls few ; spire 

 small and blunt ; aperture semilunar. Animal with long pro- 

 boscis, and large foot and mantle. 



Genus. NATICA. Shell thick and smooth ; umbilicus 

 large; callus spiral. Animal without eyes; front of foot and 

 sides with large lobes. 



Genus. NATICELLA. Aperture very wide. 



Family. NERITIDjE. Shell globular and thick ; spire 

 small ; aperture semilunar ; outer lip sharp. 



Genus. NERITA. Shell smooth or spirally grooved ; outer 

 lip thickened ; epidermis horny. Warm seas. 



Genus. NERITINA. Inner lip straight and toothed. 



Family. CERITHIDj<E. Shell long, spiral, many-whorled ; 

 aperture channeled in front. 



Genus. CERITHIUM. Shell turreted, faint varices; aper- 

 ture small, with twisted canal in front ; outer lip expanded; 

 inner lip thickened. World-wide. 



Genus. APORRHAIS. Spire long, many-whorled, and tuber- 

 culated. Short canal in front of narrow aperture. Outer lip 

 expanded, with finger-like projections. Many seas. 



Family. TURRITELLIDiE. Shell spiral or tubular; 

 upper part partitioned off. 



Genus. TURRITELLA. Shell long, many-whorled, striped 

 spirally ; aperture rounded with thin edge. Many seas. 



Genus. VERMETUS. Shell tubular and irregular ; several 

 partitions in tube ; aperture round. Many seas. 



Genus. SILIQUARIA. Shell tubular, with longitudinal slit. 

 Warm seas. 



Genus. SCALARIA. Shell turreted, many-whorled, with 

 many transverse ribs ; aperture round. Most seas. 



Family. LITORINID^. Shell spiral, opaque ; aperture 

 rounded. 



Genus. LITORINA. Shell thick, few whorls ; outer lip 

 sharp. Most seas. 



Genus. SOLARIUM. Shell target-shaped, flattened ; umbili- 

 cus very deep. Warm seas. 



Genus. PHORUS. Shell concave beneath ; flattened mar- 

 gins to whorls, often with stones and shells attached ; aperture 

 oblique ; outer lip very thin. Warm seas. 



Genus. TRUNCATELLA. Shell small, cylindrical ; aperture 

 oval and entire. Most seas. 



Family. PALUDINIDjE. Shell globular or conical ; 

 epidermis thick ; aperture round ; operculum hard. Muzzle 

 broad ; tentacles long and slender ; eyes on short footstalks. 



Genus. AMPULLARIA. Whorls round; operculum horny. 

 Muzzle long; neck with lappet on each side, forming a siphon. 

 Northern Hemisphere. 



Family. TURBINID^E. Shell spiral, pearly inside. 



Genus. PHASIANELLA. Shell long and polished ; whorls 

 convex; aperture oval and not pearly ; outer lip thin. Many 

 seas. 



Genus. TROCHUS. Shell pyramidal, base flat, many- 

 whorled; aperture pearly inside ; outer lip thin. World-wide. 



Genus. DBLPHINULA. Shell shield-like, flattened, few- 

 whorled, rough on exterior ; aperture round and pearly. Warm 

 seas. 



Family. HA LIOTIDJE. Shell spiral or ear-shaped ; aper- 

 ture very large and pearly ; outer lip notched or perforated. 



Genus. HALIOTIS. Shell ear-shaped ; spire small and 

 flat ; outer angle perforated with a row ol holes. Most seas. 



Genus. STOMATIA. Outer lip furrowed, not pierced. 

 Warm seas. 



Genus. JANTHINA. Shell spiral, thin, and translucent, 

 few-whorled ; aperture squared ; lip very thin. Vesicular float 

 attached to foot. Atlantic. 



Family. FISSURELLIDJE Shell conical and limpet- 

 shaped, front margin notched or tip perforated. 



Genus. FISSURELLA. Shell oval, tip perforated, surface 

 radiated. Most seas. 



Genus. PARMOPHORUS. Shell long and flattened, front 

 edge arched. Warm seas. 



Family. CALYPTRTEID^E. Shell limpet-like, interior 

 often with shelly process. Most seas. 



Genus. CALYPTR^EA. Shell conical, edge irregular, cup- 

 shaped process in interior. Most seas. 



Genus. PILBOPSIS. Shell conical ; apex spirally recurved ; 

 aperture rounded. Most seas. 



Family. PATELLID^E. Shell conical ; apex turned for- 

 wards. 



Genus. PATELLA. Shell oval, interior smooth ; apex 

 nearly central. World-wide. 



Family. DENTALID^E. Shell tubular, curved, regular, 

 open at each end, tapering from mouth ; aperture circular. 



Genus. DENTALIUM. As family. Most seas. 



Family. CHITONIDjE. Shell composed of eight over- 

 lapping plates, lodged in a leathery mantle, each plate with a 

 process from its front edge. 



Genus. CHITON. As family. World-wide. 



Genus. CHITONELLUS. Border velvety, exposed portions 

 of the plate small. Hot seas. 



Order. PULMONIFERA. Foot broad. Breathing 

 organ a simple chamber lined with network of respiratory ves- 

 sels. 



Section. INOPERCULA TA. Without operculum. 



Family. H ELIGIBLE. Shell external. Animal with 

 four retractile tentacles, upper pair largest and having eye- 

 specks at tips. Foot distinct ; body spiral. Respiratory aper- 

 ture on right side, under edge of shell. Mouth with horny- 

 toothed upper mandible. 



Genus. HELIX. Aperture of shell transverse, oblique, 

 rounded, or semilunar; margins distinct. Animal with long 

 foot pointed behind. World-wide. 



Genus. BUHMUS. Shell oblong or turreted ; longitudinal 

 edges of aperture unequal; columella entire. Animal like 

 Helix. Warm seas. 



Genus. PUPA. Shell oblong or cylindrical ; aperture 

 rounded. Animal with short foot, pointed behind. World- 

 wide. 



Family. LIMACIDyE. Shell small or rudimentary, inter- 

 nal, or concealed by mantle, placed over respiratory cavity. 

 Animal long ; foot not distinct. 



Genus. LIMAX. Shell internal, oblong, edge membranous. 

 Foot very long ; mantle shield-shaped ; head and tentacles re- 

 tractile. World-wide. 



Genus. TESTACELLA. Shell small, ear-shaped at end of 

 body. Back of animal with two long furrows, from which 

 others ramify. Many parts of world 



Genus. ARION. Shell oval, or made of chalky granules. 

 Tail rounded, with gland at tip. Most parts of world. 



Family. LIMN^IDJE. Shell large and thin, lip sharp. 

 Muzzle short and wide ; eyes at base of tentacles ; mouth with 

 upper mandible. 



Genus. LIMN^A. Shell spiral, rather long, last whorl very 

 wide; aperture rounded in front. Tentacles triangular. Most 

 parts of world. 



Genus. PHYSA. Spiral to left, and polished. Tentacles 

 long and slender ; edge of mantle with a deep fringe. 



Genus. PLANORBIS. Shell flattened, many whorls J aper- 

 ture semilunar. Foot round and short ; eyes at inner base of 

 tentacles. 



Section. OPERCULA TA .With an operculum. 



Order. OPISTHOBRANCHIATA. Shell small or ab- 

 sent. Branchiae towards end of body. 



