MOLLUSCA OF MICHIGAN— WALKER. 



505 



KEY TO THE GENERA OF PUPILLID^E. 



I. Shell globose, conic or depressed, heliciform; aperture with entering 



lamellae Strobilops. 



II. Shell elongated, pupiform. 



a. Lip simple, surface costate %Acanthinula. 



h. Lip thickened, surface smooth or finely striate. 



c. Aperture with outer lip regularly rounded, lower tentacles present. 

 d. Aperture edentate. 



e. Spire acuminate, lip thickened, flatly reflected Pupoides, 



ee. Spire cylindrical, obtuse, lip sharp, expanded Pupilla. 



dd. Aperture dentate, lip more or less expanded. 



e. No tooth on the columella Pupilla^ 



ee. One or more teeth on the columella Bifidaria. 



cc. Aperture with outer lip more or less contracted above the middle, 

 usually strongly indentated, lower tentacles obsolete .... Vertigo^ 



Genus STROBILOPS Pilsbry. 



Shell umbilicated, globose, conic or depressed, obliquely 

 and coarsely striated, smoother below; whorls 5 or 6, the 

 last globose; aperture Innately rounded; peristome thick- 

 ened, reflected; the parietal wall and base of the last whorl^ 

 each with two or more entering, revolving laminae. 

 ^. , , ^ , . , „ Animal quite small in comparison to the size of the shell ; 



Fig. 116. Animal of , ^ ,. ^ ■>-,-, ^ i ^ 



Strobilops. (Binney.) eye-peduncles tnick, bulbous; eyes very large. 



Jaw low, wide, slightly arcuate, ends scarcely 

 attenuated, blunt; cutting margin without 

 median projection; anterior surface with crowded 

 ribs, denticulating either margin and more de- 

 veloped on the centre of the jaw. 



Lingual membrane as usual in Helicidce, long- 

 Fig. 117. J^^ of strobilops. (Binney) ^^^ narrow, with 78 rows of 13- 1- 13 teeth mtk 



5 perfect laterals. 



Fig. 118. Dentition of Strobilops. (Binney.) 

 KEY TO THE SPECIES OF STROBILOPS.* 



I. Spire elevated, conoidal, internal lamellae on floor of body whorl 2 ta 



4, short lahyrinthica. 



II. Spire globosely elevated, internal lamellae on floor and adjacent side 



wall of body whorl, 6 or more. 



a. Six long lamellae; umbilicus a perforation merely virgo^ 



aa. About 8 short lamellae arranged in a curved radial series, umbilicus 

 wider and deep affinis^ 



* Adapted from Pilsbry, Naut. VII, 56. 



