PLANORBIS. 497 



The species has been quoted from New England to Kansas and 

 the District of Columbia. 



Planorbis parvus. 



Fig. 139. 



Shell very much compressed, almost equally concave on both sides ; whorls 

 four ; surface nearly smooth ; aperture rounded. 



Planorhis parvus, Sat, Nich. Encyc. pi. 1, fig. 5 (1817, 1818, 1819) ; Binney's ed. 45, pi. 

 69, fig. 5. — Haldeman, Mon. 27, pi. 4, figs. 19-23 (1844J. — Gould, Inv. 209, 

 fig. 139 (1841). — Adams, Shells of Vermont, 1.56 (1842). — De Kay, N. Y. Moll. 

 63, pi. 4, fig. 58 (1843). — Anon. Can. Nat. ii. 208, fig. (1857).— W. G. Binney, 

 Smith. Inst. L. and Fr. VV. Shells, ii. 133, figs. 223-225 (1865). 



Planorhis conrarns, Anthony, Cat. of Shells of Cincinnati, no descr. 



Planorbis eleratiis, Adams, Bost. Journ. Nat. Hist. iii. 327, pi. 3, fig. 16 (1840). — Gould, 

 Inv. of Mass. 207 (1841). -De Kay, N. Y. MoU. 65. 



Helix parvus, Eaton, Zool. Text Book, 195 (1826). 



Shell very small and compressed, discoidal, light yellowish horn 

 color ; right side nearly plane, but excavated at the centre ; 

 left side broadly concave ; whorls four, almost equally ex- ^'^'*^' 

 hibited on both sides, the outer one usually somewhat angu- 

 lated at its circumference ; surface minutely marked by the 

 lines of growth, shining, clear ; aperture rounded, rather '^vuZ 

 longer than broad, not inclining to either side, its plane very 

 oblique ; lip sharp, slightly reflected on the left side ; within bluish- 

 white. Greatest diameter, one fourth of an inch ; lesser diameter, 

 one fifteenth of an inch ; but generally much smaller. 



Animal wdiitish, dusky above, with a still darker line at tip of 

 tentacula. 



Abundant in brooks and ponds. 



This is the smallest shell of the genus which we have, unless, 

 perhaps, it be P. exacutus, which is commonly found of as small a 

 size. It is not difficult to be recognized by its regular figure, and 

 its very thin, compressed appearance. P. deflectus^ exacutus, and 

 hi?'sutus, all have marked peculiarities, which at once separate them 

 from this undistinguished species. 



Said to inhabit the whole of Eastern North America. 



Fossil in post-pleiocene of Ottawa Yalley. 



Planorbis elevatus. 



Shell small, whorls three or four, swelHng above, with the apex sunken, deeply 

 concave beneath ; aperture slightly oblique. 

 32 



