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 keel; 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. I Dorset Cat. pi. 20..f. 13. 



Shell flattish, semitwnsparent, reddish or blackish horn- 

 color, becoming white with age, concave on one side aind 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 

 ftttle oblique downwards ; inner lip slightly spread on the 

 body, whitish at the angles and round the inner-margin : 

 "diameter an inch or father more. 



Ponds and old water-courses, v. v. 



' 7- Helix spirorbis. Spiral Snail-sheH. 



Montagu, pi. 25. f. 2 Dorset Cat. pi. 20. f. 17- 



Shellflat, brown horn-color, concave on both sides : spires 

 six, rounded and close-set, finely striate across : aperture 

 bval, 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 

 .en the body volution. 



Ponds and still waters, v. v. . 



8. Helix rhombea. RhomMc Snatt-shett. 



Shell flat, semitransparent, a little concave on both sides, 

 whitish or tinged with rufous, often covered with a rough 

 brown ,skin : spires four, smooth, well denned by the line 

 of separation, the larger volution compressed or flattened 

 on the back so as to give it a slightly carinated appearance 

 at the edge on both sides, which however is muqh -stronger 

 underneath : aperture obliquely rhombic, in consequence 



of 



