CYCLOSTOMA. MOLLUSCA. 55 



pressed on both sides., with a keel round the middle of the body 

 whorl. ^ inch in diameter. Inhabits Europe in stagnant waters. 

 Brown's Illusl. pi. 41, fig. 35, 36, 37, 38. 



P. spirorbis, Lam. Shell horn-coloured, discoid, concave on both 

 sides, with six rounded whorls. 3 lines in diameter. Inhabits fresh 

 waters in Europe. B Mont. pi. 25, fig. 2. 



P. vortex, Lam. Shell reddish brown, carinated, with the upper 

 side concave and the base flat j aperture oval and compressed. 

 3 lines in diameter. Fresh waters in Europe. Mont. pi. 25, fig. 3. 



FAMILY X. COLIMACEA. 



Spin valve, with no projecting parts on the exterior, except the 

 markings of increase, and with the right margin of the open- 

 ing often reflected outwards ; terrestrial, with cylindrical ten- 

 tacula, and with or without an operculum. 



All the Colimacea are terrestrial, and respire air. Their tentacula are cylindrical, 

 to the number of four in the greater part, and two in the others. Though most of 

 them are destitute of an operculum, yet in winter many close up the aperture with 

 a calcareous plate, which, however, does not adhere to the animal. The genera with 

 two tentacula are Cyclostoma and Auricula ; those with four tentacula, Succinea, 

 Achatina,) Bulimus, Clausilia, Pupa, Helicina, Anastoma, Carocolla^ and Helix. 



* With two tentacula. 

 Gen. 68. CYCLOSTOMA, Lam. Helix, Lin. 

 Shell of variable form, with the whorls of the spire rounded ; 

 aperture round, regular, with the margins united circularly, 

 and reflected in age ; an operculum. 



The shells of this genus vary much in their general form, according to the species. 

 Some are of a flattened shape, others conical or turreted ; and a few cylindrical. 

 They have all a horny operculum. The animal has two cylindrical tentacula, with 

 the eyes at the external base. 



C. volvulus, Lam. Shell trochiform, deeply umbilicated, transversely 

 striated, and variegated with red and white ; spire acuminated ; 

 aperture white or yellow , margin of the lip reflected. 1 J inch 

 in diameter. Lister, pi. 50, tig. 48. 



C. labeo, Lam. (Nerita, Muller.) Shell oblong, obtuse, umbili- 

 cated, pellucid, with white or reddish decussated striae, and a 

 transverse series of small yellowish forked spots ; margin of the 

 lip reflected, white. 1^ inch long. Jamaica. Lister, pi. 25, fig. 23. 



Gen. 69. AURICULA, Lam. Valuta, Helix > Lin. 

 Shell suboval or oval oblong ; aperture longitudinal, entire at 

 the base and narrowed above, or with the border disunited ; 

 columella with one or many folds ; lip sometimes reflected 

 outwardly, sometimes simple. 



A. Midce, Lam. Shell ovate-oblong, very thick, with decussated 

 striae, and granulated above ; epidermis fuscous chestnut ; spire 

 short, conoid ; aperture somewhat ear-shaped ; pillar with two 

 teeth. 4 inches long. Inhabits India Lister, pi. 1058, fig. 6. 



A. scarabceus, Lam. Shell ovate, convex, depressed, the sides an- 



