60 



animal possesses the faculty of crawling on the surface of the water, 

 in a reversed position, the shell downward. 



Geuus Lymn^A. — Shells subovate, oblong or somewhat taper- 

 ing. Aperture entire, longitudinally oblong, the right lip circu- 

 larly joined to the left at the base and folded back on the pillar. 



Lymn^a columella. — Shell thin, fragile, hom-color ; whorls 

 four, longitudinally wrinkled. Spire prominent, acute. Suture 

 not much impressed. Aperture dilated, ovate. Columella much 

 narrowed near the base, so that the view may be extended from the 

 base almost to the interior apex of the shell. Length seven-tenths 

 of an inch nearly; of the spire one-quarter of an inch. 



Inhabits stagnant waters and miry places. Collection of the 

 Academy. 



Animal aquatic, base not so long as the aperture ; dusky, with 

 small whitish spots ; tentacula broad, pyramidal, compressed ; eyes 

 small, black, placed at the inner base of the tentacula. 



This species is allied to L. catascopium of the American edition 

 of Nicholson's Encyclopedia, but the revolution of the whorls is 

 more oblique, the shell thinner, the aperture much more dilated, 

 and the columella differently formed. For several specimens of 

 this shell I am indebted to Mr. Titian Peale. 



[J. A. N. S. vol. i. p. 124, et seqq., Oct., 1817.] 



Genus Ancylus. — Shell conic, not spiral, concave beneath, 

 above with a simple apex. Animal with the eyes placed at the 

 inner base of the tentacula. 



Ohs. This genus has been by writers confounded with the 

 PatettFC. The European species are Patella lacnstris andjluviatt- 

 lis of Linn6. 



Ancylus rivularis. — Shell corneous, opake, conic-depressed, 

 apex obtuse, nearer to, and leaning towards, one side and one end ; 

 aperture oval, rather narrower at one end, entire ; within milk- 

 white. 



Length one-fourth of an inch. Cabinet of the Academy. 



Common, adhering to stones in rivulets ; the animal resembles 

 the inhabitant of shells of the genus Lynvnsea, the tail is veiy ob- 

 tuse, rounded. 



