46 HELIX. SNML-SHELL. 



Shell flat, seraitransparent, 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 the 

 other : diameter about half an inch. 



It differs from the next, in having the circular ridge 

 round the margin of the body volution placed exactly in th 

 middle, giving the shell a more convex appearance ; in the 

 paler color and greater fragility 3 and in the aperture being 

 pval. 



Stagnant waters, and slow streams, v. v. 



4. Helix complanata. Flattened Snail-shell. 



Lister, pi. 138. f. 42 Montage pi. 25. f. 4. 



Helix limbata. J) a Costa, pi. 4. f. 10, and pi. 8. f. 8. 



Helix planorbis. Pennant, pi. 86. f. 2 Linn. Trans, viii. 

 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 oblique, one lip reaching further down 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 not in 

 the middle of the margin but at the base, the under side of 

 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, v. v. 



5. Helix Vortex. Whirled Snail-shell. 



Lister, pi. 138. f. 43 Pennant, pi. 86, f. 4 Da (?ota, 

 pl. 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 denned 

 ppires, the largest one with a slight ridge round the mar- 

 gin 



