HELIX. SNAIL-SHELL. 47 
gin near the base: aperture nearly oval, compressed, rather 
acute towards the top : diameter hardly half an inch. 
It differs from the two last in the number and compact¬ 
ness of the volutions. 
In ponds and ditches, v. v. 
B. Without heel; perforated or concave. 6 to 36. 
* 6 . Helix cornea. Horn Snail-shell. Fig. 52. 
Lister , pi. 137. f. 41— Pennant , pi. 86. f. 3— Da Costa, 
pi. 4. f. 13 -—Donovan, pi. 39. f. 1— Dorset Cat. pi. 20. f. 13. 
Shell flattisli, semitransparent, reddish or blackish horn- 
color, becoming white with age, concave on one side and a 
little depressed on the other: spires four or five, separated 
by a deep line, the first large and well rounded, wrinkled 
across, with often a larger transverse ridge or two not far 
from the aperture : aperture somewhat crescent-shaped, a 
little oblique downwards ; inner lip slightly spread on the 
body, whitish at the angles and round the inner-margin : 
diameter an inch or rather more. 
Ponds and old water-courses, v. v. 
7. Helix spirorbis. Spiral Snail-shell. 
Montagu , pi. 25. f. 2— Dorset Cat. pi. 20. f. 17. 
Shellfiat, brown liorn-color, concave on both sides: spires 
six, rounded and close-set, finely striate across : aperture 
oval, sometimes inclining to circular, but always attached 
to the body volution at the sides, a little oblique : diameter 
about a quarter of an inch. 
It differs from H. Vortex, in not having any ridge or keel 
on the body volution. 
Ponds and still waters, v. v. 
8 . Helix rhombea. Rhombic Snail-shell. 
Shellfiat, semitransparent, a little concave on both sides, „ 
whitish or tinged until rufous, often covered with a rough 
brown skin: spires four, smooth, well defined by the line 
of separation, the larger volution compressed or flattened 
on the back so as to give it a slightly catenated appearartce 
at the edge on both sides, which however is much stronger 
underneath: aperture obliquely rhombic, in consequence 
