PLANORBIS. 211 



26. PLANORBIS PARVUS, Say. 

 Hald. Monog. p. 27, t. 4, f. 19—23. 



Planorhis Billingsii, Lea. Plate 7, fig. 10. 



Mr. Lea's species is said by its author to 

 differ from parvus in having a wider umbili- 

 cus, more oblique aperture, and exhibiting one 

 more whorl ; but in neither of these respects 

 does it differ from the majority of fully grown 

 specimens of parvus. 



27. PLANORBIS ARCTICUS, Beck. 



Plate 7, fig. 11, 12, 13. 



Shell corneous or yellowish, widely umbili- 

 cate ; whorls three and a half, canaliculately 

 sutured, the last one obsoletely angulate at 

 the periphery ; aperture oblique. 



Diam. 5, alt. 1"5 mill, 



Greenland. 



I have not seen this species, which is said 



by Morch to resemble both PL parvus and 



PI. defiectus. 



(58) 15 



