﻿io7 Paleontology 29 



The species is represented by a number of shells. The largest of 

 these has a width of 10 % mm. and a length of 9^ mm. The 

 small size, depressed shell, and extended beak in the pedicle 

 valve serve to distinguish it from Airy pa spinosa of the ordinary 

 type. A. mis sour iensis, which is associated with it, is readily 

 distinguished by its more numerous and much finer striae. 



Locality. — Livingston, Montana. 



Airy pa hystrix var. occidentalis (Hall) 

 PIT fig. 4. 



This species is represented by several specimens of imperfect 

 shells characterized by 10 to 20 very coarse nodose plications on 

 each valve. 



Locality. — Princeton, Montana. 



Airypa missouriensis Miller. 

 PL I figs. 7-7b. 



Shell small subcircular, the valves nearly equally convex. 



Greatest convexity of the pedicle valve in the umbonal region, 

 from which it slopes regularly to the sides. Beak of the pedicle 

 valve pointed, but slightly incurved and extending beyond the 

 hinge line. Area small. 



Pedicle valve in general uniformly convex, but in some speci- 

 mens with a slight undefined depression along the median line 

 from the umbone to the front. Beak small and incurved. 

 Surface covered by 40 to 80 fine bifurcating striae. Fold and 

 sinus absent. Average specimens have a length and breadth of 

 about 9 mm. and a thickness of 3% mm. 



Locality. — This is a rather abundant shell at Princeton, 

 Montana. 



Athyris parvula Whiteaves. 

 PL III figs. 2-2C. 



Four specimens represent this species. The largest has a 

 length and breadth of 9 mm. and has the fold and sinus rather 

 more prominently developed than indicated in Whiteaves' 33 



^Contribution to Canadian Paleontology, vol. I, pt. 3, 189 1, pi. 32, 

 Figs. 4 and 5. 



