THE NATURAL HISTORY SURVEY. 



155 



central tooth long and rather narrow, base of attachment exca- 

 vated on the lower border; reflection long and narrow, unicuspid, 

 but there are side bulgings representing the side cusps; first six 

 lateral teeth similar to central tooth, but wider; next seven teeth 

 with a small outer wide cusp; the fourteenth tooth has a bulging 

 on the lower part of the inner cusp; from this point the teeth 

 become narrower to the forty-second tooth, when they widen 

 and develop an inner small cusp and two outer side cusps; the 

 marginals are very variable, and the outer side cusps may or 

 may not be developed; the forty-first tooth was very peculiar 

 on a membrane having but 47-1-47 teeth (some of the mar- 

 ginals probably torn away), and this tooth was found on all the 



FIG. 21. 



Radula of POLYGYRA EXOLETA Binney. (Original.) c, central tooth 

 1, first lateral; 7, lateral tooth, showing appearance of outer cusp; 14, 

 marginal tooth; 23, 32, intermediate marginal teeth; 41, 42, 45, outer mar- 

 ginal teeth. 



rows of teeth and on both sides of the membrane. The outer 

 cusp of the lateral teeth is very variable. Binney found 

 eleven perfect laterals, but remarked that the eighth tooth 

 showed some modification (Fig. 21). 



Genitalia: "The penis sac is very stout, long, cylindrical, 

 receiving the retractor muscle and vas deferens at its summit; 

 genital bladder subconical, on a short, small duct; the vas def- 

 erens is convoluted as it leaves the prostate." These organs 

 are specifically distinct from those of albolabris, and serve as a 

 sure method of distinguishing the two species. 



Distribution: Western New York west to Iowa, Michigan 

 south to Alabama and Georgia. 



Geological distribution: Pleistocene of central United States; 

 Loess. 



Habitat: Same as that of albolabris. 



