PLANORBIS. 497 



Tlie species has been quoted from New England to Kansas and 

 the District of Cohnnbia. 



Planorbis parvus. 



Fig. 139. 



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

 four; surface nearly smooth ; aperture rounded. 



P/annrbis parvus, Say, Nich. Encvc. pi. 1, %. 5 (1817, 1818, 1819) ; Bikxey'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). 



Planoi-liis concavus, Anthony, Cat. of Shells of Cincinnati, no descr. 



P/anorbis ekvatus, Adams, Best. Journ. Nat. Hist. iii. 327, pi. 3, fig. 16 (1840). — Gould, 

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



Htlix 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 \Z'^'^' 

 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 incli ; but generally much smaller. 



Animal whitisli, 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 

 hirsutus, 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 Valley. 



Planorbis elevatus. 



Shell small, whorls three or four, swelling above, with tlie apex sunken, deeply 

 concave beneath ; aperture slightly oblique. 

 32 



