PELECYPODA—PRIONODESMACEA. 



517 



CXII. Whiteavesia Ulrich. 



Very similar to Modiolopsis but differs in its thinner hinge plate 

 and shell, in the convex basal outline and absence of a mesial fur- 

 row. From Orthodesma it also differs in these last two character- 

 istics as well as in its tightly closing instead of gaping valves. 

 Ordovicic. 

 422. W. modioliformis Meek and Worthen. (Fig. 695, d.) 



Ordovicic. 



Shell obliquely oval, marked with rather strong concentric 

 wrinkles especially anterior to the umbo. 



FlG. 695. a, &, Colpomya constricta, right and left valves ; c, Whiteavesia cincinnat- 

 iensis, right valve ; d, W. modioliformis, left internal mold. (Minn. Surv. ) 



Stones River of Wisconsin, Minnesota ? 



423. W. cincinnatiensis Hall and Whitfield. (Fig. 695, c.) 



Ordovicic. 



Surface marked with numerous, irregular concentric and faint 

 radiating lines. Type of genus. 



Eden of Ohio, etc. 



CXIII. Eurymya Ulrich. 

 Somewhat triangular, with broad and wing-like posterior, and 

 greatly narrowed anterior end. Base oblique. Hinge line straight. 

 Beaks small, near anterior extremity. Hinge with obscure cardi- 

 nal tooth in left valve and corresponding depression in right, and 

 with broad and longitudinally striated ligament area posterior to 

 the beaks. Muscle impressions as in Modiolopsis. Differs from 

 Modiolopsis and Modiontorpha in the wing-like posterior extremity 



