66 Review of the New York Geological Reports. 
*s. 
. 
re 
~ abt Tee ee | 
* 
Hall’s Report, p. 207. 
Fig. 1, a, 6, ¢, d. Delthyris granulifera. 
F 
not quite so numerous, and the beak of the fissured valve does 
not overhang the cardinal area. These differences are, probably, 
variations depending on age, geographical distribution and litho- 
ogical peculiarity, rather than essential specific distinctions. 
Both at t alls of the Ohio and the southern part of the 
Du Buque district of Iowa, these western rocks contain another 
Delthyris allied to the above, but, for the most part, having a 
narrower cardinal area; but a recent inspection of a number of 
individuals, induces us to believe that this Delthyris passes by 
