PLANORBIS ARMIGERUS. 31 



SYNONYMS AND REFERENCES. 



P. ARMIGERUS, SAY. Journ. Acad. Nat. Sc., vol. 2, p. 164. 

 " " GOULD. Invert, of Mass., p. 205, fig. 138. 



DESCRIPTION. 



ANIMAL "very active, of a blue-black or slate 

 color; foot long and narrow: respiratory groove 

 very acutely pointed." Gould. 



SHELL polished, with four subcylindrical whirls, 

 subcarinated upon the left side, and having the 

 lines of accretion very fine: right side nearly 

 plane, the centre slightly impressed: left side 

 widely and deeply umbilicated, and exhibiting 

 all the volutions: aperture subrotund, oblique, 

 armed far within (a fig. 12) with six white teeth, 

 which nearly close the aperture, the largest thin 

 and oblique, running backwards from the left to 

 the right side, (fig. 15,) on the left of this is a 

 small one, and around the vault four others, 

 gradually increasing in size from the left to the 

 right side. 



COLOR light brown; peritreme and an occa- 

 sional varix, much darker. 



GEOGRAPHICAL DISTRIBUTION. Eastern, mid- 

 dle, and western states, and the Northwest Ter- 

 ritory. 



