168 THE CHICAGO ACADEMY OF SCIENCES. 



central tooth with a base of attachment longer than wide, the 

 base excavated and thelower outer corners much expanded; re- 

 flection tricuspid, the central cusp long and wide, very nearly 

 reaching the lower margin of the base of attachment, side 

 cusps very short; lateral teeth similar to the central tooth, but 

 bicuspid, the inner cusp much the larger; marginals Variable, 

 at first similar to laterals, but soon the inner cusp (twenty) be- 

 comes bifid, changes into a perfect cusp (twenty-three trifid), 

 and finally the reflection becomes very narrow and with three 

 cusps, of which the central one is the largest (Fig. 27). There 

 are about 100 rows of teeth. fJinney gives 211-21 and Morse 

 28-1-28 teeth. 



Genitalia; "The characteristic feature of the genitalia is 

 the penis sac. It is unproportionally long, club-shaped, and 

 greatly enlarged above, where it receives both vas deferens 

 and retractor muscle. The genital bladder is small, elongate- 



FIG. 27. 



Radula'of POLYGYRA MONODON FRATERNA Say. (Original.) c, central 

 tooth; 11, first marginal tooth; 16, 17,20, intermediate marginal teeth; 23, 

 27, 29, outer marginal teeth. 



oval, on a short, delicate duct. The epididymis is convoluted 

 in its whole length." (W. G. Binney.) 



Distribution: Canada to Minnesota, south to North Caro- 

 lina and San Antonio, Tex. (Pilsbry.) 



Geological distribution: Pleistocene of the Mississippi Val- 

 ley; Loess. 



Habitat: Found sparingly under pieces of bark, chips, logs, 

 etc., in open patches of woodland or in meadows. The variety 

 in this area does not congregate together but is found either 

 singly or with one or two companions. Associated sometimes 

 with P. thyroides and Pyramidula alternata. 



