THE NATURAL HISTORY SURVEY. 



147 



The teeth are like those of tridentata, excepting that there are 

 eleven perfect laterals, and all the inner cusps are simple until 

 the seventeenth marginal, which is bifid. Binney (Manual, 

 p. 292) gives 40-1-40 teeth with twelve perfect laterals. The 

 writer is certain that his count was correct, as the teeth were 

 recounted several times, always with the same result. The 

 membranes were perfect (Fig. 17). 



FIG. 17. 



Radula of POLYGYRA FRAUDULENTA Pilsbry. (Original.) c, cen- 

 tral tooth; 1, first lateral; 10, outer lateral; 13, first marginal; 16, 20, mid- 

 dle and outer marginals. 



Genitalia: Similar to that of tridentata, but "the duct of 

 the genital bladder is of equal size throughout its length an 

 unimportant, even if a constant difference." (Binney.) 



Distribution: Ontario, Canada, to Michigan and Illinois, 

 south to Georgia. (Pilsbry.) 



Geological distribution : Pleistocene; Loess. 



Habitat: Same as tridentata, and frequently associated 

 with that species. 



Remarks: This species has long been known under the 

 name "fallax Say," but Professor Pilsbry has shown (1. c., p. 21), 

 that this is not the true fallax of Say, that species being the 

 introferens of Bland. It is easily distinguished from tridentata 

 by its elevated spire and strongly armed aperture, and is more 

 common than that species. The animal is very timid in cap- 



