GIRTY, THE WEWOKA FORMATION OF OKLAHOMA 131 



strong on each side, but there may be four or six. Three is the usual number 

 for the fold, but four and even Ave occur in rare instances. Individuals with 

 three mesial plications and four laterals, especially when one or two of the 

 latter are immature or imperfectly developed, might equally well be placed 

 under P. osagensis itself. Apparently this variety has been referred by 

 authors to osagensis unqualifiedly, but I believe it can be distinguished to 

 advantage. 



This form resembles P. osagensis var. occidental is, which is, however, 

 a much larger species, with on the whole, more numerous mesial plica- 

 tions, and it occurs in very different faunal associations. 



Horizon and locality: Wewoka formation: Coalgate quadrangle, Okla. 



Pelecypoda 

 Nucula wewokana sp. nov. 



Shell small, triangular; width slightly, though distinctly, greater than the 

 height. Beaks set well toward the posterior end. toward which they more or 

 less distinctly point. The convexity is high. The cardinal and posterior ends 

 are abruptly flattened or depressed into a usually well-defined escutcheon and 

 lunule. The ventral border is regularly rounded. The anterior and cardinal 

 lines are straight or gently convex according as the lunule and escutcheon are 

 flat or project somewhat from the abrupt infolding of the shell along the two 

 edges. The anterior end is strongly rounded; the posterior is subangular. 



The surface is finely, sharply and regularly striated. 



This species is related to N. parva McChesney, with which, in fact, I at 

 first identified it. It differs, to judge by the figures of McChesney and 

 of Meek and Worthen, in being less transverse and in having the shell at 

 the posterior or shorter end less strongly projecting. N. wewokana is 

 also very similar in outline to N. pulchella Beede and Eogers, but N. pul- 

 chella is said not to have a distinct lunule and the posterior end seems to 

 be abruptly truncated. In the present species, the shell projects a little, 

 so that the outline at this end is usually gently convex and formed by the 

 edge of the shell, whereas in N. pulchella, it is straight and formed by 

 the angle of flexure, which either overarches the margin or is coincident 

 with it when viewed from above. 



Horizon and locality: Wewoka formation; Wewoka quadrangle, Coal- 

 gate quadrangle, Okla. 



Anthraconeilo subgen. nov. 



The shells included under this title are rather large, strongly transverse, very 

 inequilateral, considerably produced anteriorly. The beaks point toward the 

 shorter side. Shell closed all annual. Dentition taxodont with a great many 



