The Nautilus. 



Vol. XXIII. MAY, 1909. No. 1. 



NOTES ON PLANORBIS II : P. BICARINATUS. 



BT BRYANT WALKER. 



Planoebis BICARINATUS Say. PI. I, fig. 3. 



1817. Planorbis bicarinatus Say, Nich. Encyc, pi. i, f. 4. 



1822. Helix angulata Rackett, Lin. Tr. xiii, p. 42, pi. v, f. 1. 



1834. Planorbis engonatus Conrad, N. F. W. Shells, sup. p. 8, 

 pi. ix, f. 8. 



1834. ? Planorbis antrosus Conrad, Am. J. Sc. (1) xxv, p. 343. 



1861.? Planorbis lautus H. Adams, Proc. Zool. Soc, Lond. 1861, 

 p. 145. 



This common and well-known species is one of the characteristic 

 species of the fresh-water pulmonate fauna of eastern North America. 

 It stands quite by itself, having, with the exception of the recently 

 described P. eucosmius Bartsch from North Carolina, no closely 

 related species in our fauna. It is the type of the subgenus HeUsoma 

 Swainson. 



The shape of the shell is so well marked and distinctive that the 

 synonymy is, as shown above, comparatively small. The Helix 

 angulata of Rackett was, in all probability, described in entire igno- 

 rance of Say's previous description. 



The type of Conrad's P. engonatus seems to have disappeared. 

 According to Haldenian, who saw the " single original specimen," 

 then in the collection of a Mr. Mason, it was a monstrosity. Con- 

 rad's figures are poor, but Haldeman's (Mon., pi. i, figs. 5 and 6), 

 which are apparently excellent, confirm his opinion. It was found 



