46 
HELIX. SNAIL-SHELL. 
. Shell flat, semitransparent, pale horn-color with some¬ 
times a rufous tinge, concave on both sides : spires four or 
five, a little sloping on each of the sides, finely striate 
across ; the largest with a slight prominent ridge placed 
exactly in the middle of the margin : aperture compressed, 
with a rather acute termination at the upper end; the 
lower end oblique, one side being more elongated than tie 
other : diameter about half an inch. 
It differs from the next, in having the circular ridge 
round the margin of the body volution placed exactlyinthe 
middle, giving the shell a more convex appearance; in the 
paler cQlor and greater fragility ; and in the aperture being 
pval. 
Stagnant waters, and slow streams, v. v. 
* '4. Helix complanata. Flattened Snail-shell. 
Lister , pi. 138. f. 42— Montagu, pi. 25. f. 4. 
Helix limhata. Da Costa, pi. 4. f. 10, and pi. 8. f.& 
Helix planorbis. Pennant, pi. 86. f. 2— Linn. Tram, riil 
pi. 5. f. 13 —Dorset Cat. pi. 14. f. 8, and pi. 20. f. 10. 
Shell flat, semitransparent, brown, chesnut, or nearly 
black, concave on both sides : spires four or five, rather 
rounded, slightly striate across; the largest with a faint 
prominent circular ridge round the margin and placed at 
the base, and all well defined by the line of separation: 
aperture pblique, one lip reaching further dpwn the volu¬ 
tion than the other, rather rounded at the top: diameter 
more than half an inch. 
In consequence of the keel or ridge being placed noth 
the middle of the margin but at the base, the under sideof 
the volution does not slope so much down to the edge as 
the upper, giving the shell a flatter appearance; and con¬ 
sequently the upper edge of the lip is not so acute. 
Ponds, ditches, and stagnant waters, t?. i?. 
5. Helix Vortex. Whirled Snail-shell. 
Lister , pi. 13S. f. 43-r-Pe.inant, pi. 86. f. 4 —Da Ma } 
pi. 4. f. 12— Donovan, pi. 75 —Dorset Cat. pi. 20. f. 12. 
Shell very flat, semitransparent, horn-color, concave on 
one side, with six or seven close-set and well defined 
spires, the largest one with a slight ridge round the mar- 
gin 
