HELIX. SNAIL-SHELL. 
44 
gitudmally, 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; 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 con- j 
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- 
(and, and North Britain, v. m . 
HELIX. SNAIL-SHELL. 
Shell with a single valve, spiral, more or less 
transparent and brittle: aperture contracted, 
roundish pr crescent-shaped. 
Obs. There ever has been, and probably ever will be, a 
difficulty in makiug 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 any 
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 heel-like ridge. 1 to 5. 
B. Not keeled, but perforated or concave. 6 to 37. 
C. The volutions rounded: imperforated at the base. 38 j 
D. Shell tapering. 44 to 51. 
E. Shell oval , without perforation. 52 to 65. 
A. Flattened, with an acute keel-like ridge. 1 to 5. 
I. Helix lapicida. Bock Snail-shell. Fig, 59, 60. 
Lister , pi. 69. f. 68 — Pennant , pi. 86 . f. 1—Da 
ph 4. f. 9— ■ Donovan , pi. 39. f. 2— Dorset Cat. pi. 20. f.9. 
; ' ' ' Shell 
