164) NEW YORK STATE MUSEUM 



slightly if at all less conspicuous on the lateral slopes than on 

 other parts of the shell. Small specimens, probably the young 

 of this species, have a distinct median depression on the brachial 

 valve. These shells have distinct radiating striae, while many 

 of the same size in the shales show only faint traces of striae. 



CRYPTONELLA Hall 



Cryptonella rectirostris Hall 



Pal. N. Y. 4:394, pi. 61 



The species is represented in bed VII by several partially 

 exfoliated pedicle valves. The dimensions of an average speci- 

 men are, length 4.6 mm, width 13 mm. 



Cryptonella planirostris Hall 



Pal. N. Y. 4:395, pi. 61 



A single large specimen was found in bed VIII. It is easily 

 recognized by the angular margins of the umbonal slopes, and 

 the flattened areas on either side of the deltidial plates. 



TROPIDOLEPTUS Hall 



Tropidoleptus carinatus (Conrad) 



Pal. N. Y. 4:407, pi. 62 



This species is fairly represented in the lower shales, but only 



one specimen has been found in the limestone. The shell in bed 



V is much smaller than the average Hamilton specimen, but is 



similar in form and size to the majority of those found in the 



shales at Plumbottom creek. It is 7 mm long, by 8.2 mm wide. 



The largest specimen found in the shales has a length of 9 mm 



and width of 10.5 mm. 



atrypa Dalman 



Atrypa spinosa Hall 



Pal. N. Y. 4:322, pi. 53a 



One rather small shell of this species was found in bed V. 

 The strong radiating plications and projecting concentric lamel- 

 lae are preserved. 



