~ 
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 centraltooth, but wider; next seven teeth 
with asmall outer wide cusp; the fourteenth tooth hasa 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 
Fie. 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. 
