THE GASTROPODA 187 



mantle produced anteriorly into a cervical lobe ; foot with a posterior 

 dorsil mucous pore. Orpiella, Gray ; differs from Ariophanta in 

 having a horn-shaped protuberance at the hinder extremity of the foot. 

 Vitrina, Draparnaud ; the mantle projects in front and on the right 

 side, and partially overlaps the thin and depressed shell ; foot elongated, 

 without a posterior mucous pore ; British. Helicarion, Ferussac ; differs 

 from Vitrina in having the foot truncated anteriorly, with a posterior 

 mucous pore. FAMILY 3. LIMACIDAE, Gray. Shell almost completely 

 covered by the mantle, or internal. Parmacella, Cuvier ; shell unguifonn 

 with a spiral summit ; the mantle occupies the centre of the body and 

 completely covers the shell except for a very small orifice above the spire. 

 Limax, Linnaeus ; shell wholly internal, without a spiral summit ; 

 mantle reduced, and situated on the anterior part of the body ; 

 pulmonary aperture towards the hind end of the pallial border ; British. 

 Urocyclus, Gray ; shell oval, without a spire, internal except for a small 

 median orifice in the hinder part of the mantle ; pulmonary aperture 

 in the middle of the pallial border ; African. Parniarion, Fischer. 

 Amalia, Heynemann. Ayriolimax, Morch. Mesolimax, Pollonera. Mono- 

 chroma, Simroth. Paralimax, Bottger. Metalimax, Simroth. FAMILY 4. 

 PHILOMYCIDAE, Fischer. No shell ; the mantle covers the whole surface 

 of the body ; radula with squarish teeth. Genus Philomycus, Ferussac; 

 foot broad ; genital orifice near the right tentacle. FAMILY 5. 

 OSTRACOLETHIDAE, Simroth. Shell largely chitinous, not spiral, its 

 calcareous summit projecting through a small hole in the mantle which 

 elsewhere covers it. Genus Ostracolethe, Simroth. FAMILY 6. ARIONIDAE, 

 Gray. Shell internal or absent ; animal limaciform ; mantle restricted 

 to the anterior and middle part of the body ; radula with squarish 

 teeth. Genera Arion, Ferussac ; respiratory orifice at the anterior end 

 of the pallial border ; genital orifice close to the respiratory orifice ; shell 

 reduced to simple isolated calcareous granules ; British (Fig. 172, D). 

 Geomalacux, Allmaiin ; shell internal, oval ; Ireland. Ariolimax, Morch. 

 Anadenus, Murch. FAMILY 7. 

 HELICIDAE, Gray. Shell with 

 medium spire, external or par- 

 tially covered by the mantle ; 

 mandible folded ; radula with 

 square teeth ; genital orifice below 

 the right posterior tentacle ; geni- 

 tal apparatus generally provided 

 with .a dart- sac and multifid 

 vesicles. Genera Helix, Lin- FIG. 177. 



IiaeilS ; shell globular, conical or Helix nemoralis, right-side view. I, anus; II, 



depressed, with a rounded or ex- ! ^ff^JlS^- SS&^. 



panded aperture (Figs. 172, A imeumostome in its maximum distension. 



and 177) ; British. (A large 



number of sub-genera has been established, which includes more than 

 4000 species : Polyyyra, Say. Sagda, Beck. Pleurodonta, Fischer von 

 Waldheim. Helicodonta, Ferussac. Helicophanta, Beck. Acamis, Mont- 

 fort. Sitala, Adams. Chlorites, Beck. Hapalns, Albeis, etc.) Bulimus, 



