44 HELIX. SNAIL-SHELL. 



gitudinally, ribbed or wrinkled transversely, with a longi- 

 tudinal ridge near the thicker margin beset with tubercles, 

 which towards the thinner end become larger flat and con- 

 cave, the last six or eight of them perforated ; the other 

 end with a single slightly raised spire, surrounded circu- 

 larly with a continuation of the gradually decreasing tuber- 

 cles, and ending in an obtuse point j below the ridge is a 

 furrow and a small rib, behind which the margin is rounded 

 and turned in ; the outer margin very thin and plain '. color 

 reddish-brown, sometimes spotted or marbled ; inside cpn- 

 cave, glossy and richly perlaceous : length sometimes four 

 inches, and three in breadth. 



Guernsey and Jersey, on rocks at low-water mark ; 

 rarely thrown up on the western coasts, Bullock in Ire- 

 land, and North Britain, v. m. 



HELIX. SNAIL-SHELL, 



Shell with a single valve^ spiral, more or less 

 transparent and brittle : aperture contracted, 

 roundish or crescent- shaped. 



Obs. There ever has been, and probably ever will be, & 

 difficulty in making precise and definite limits between this 

 family and that of the Turbo. It may therefore be neces- 

 sary to understand, that all which have an orbicular aper- 

 ture, however transparent and brittle they may be, are 

 ranged with the latter genus. The student who finds ar*y 

 difficulties on this point, will, by turning to the proper di- 

 vision of each family, easily have his difficulties removed. 



A. Flattened, with an acute keel*like r ridge. 1 to 5. 



B. Not keeled, but perforated or concave. .6 to 3,7 



C. Tlie volutions rounded : imperforated at the bpse. 38 



to 43. 



IX Sfiell tvpwing. 44 to 51. 

 E. Shell oval, without perforation. 52 to 65. 



A. Flattened, with an acute keel-like ri4ge. I*toi5. 

 1. Helix lapicida. Rock Snail-nheU. Fig. 59, 60. 

 Lister, pi. 69. f. 68 Pennant, pi. 86. f. 1 > Costa, 

 pi. 4. f. 9Donovan, ,pl, 39. f. 2-rZtamtf CM. pi. 20. f. 9. 



Shell 



