PELECYPODA—PRIONODESMACEA, 



397 



Ripleyan of New Jersey (Cliffwood-Wenonah), Maryland, 

 North Carolina, Alabama, Mississippi, Texas. 



78. N. whitfieldi Weller. Cretacic. 

 Differs from A r . percrassa in the absence of radiating costae and 



marginal crenulations. 



Ripleyan of New Jersey (Cliffwood-Red Bank). 



79. N. ovula Lea. (Fig. 507.) Eocenic. 

 Margin very minutely crenulated. 



Maryland (Aquia), Alabama (Midway and Lignitic). 



XXVII. Nuculites Conrad. {Cleidophovus Hall.) 

 Differs from Nucida in the absence of the resilifer beneath the 

 beak, the row of teeth extending without interruption from the 

 anterior muscle scar to the posterior, and 

 in the presence of a nearly or quite verti- 

 cal partition internally, separating the ante- 

 rior muscle scar from the cavity of the shell 

 and extending about two thirds the distance 

 from beak to base. This partition leaves a 

 deep furrow on the casts of the interior of 

 the shell in which condition specimens of 



Fig. 507. Nucula ovula. 

 (Md. Geol. Surv.) 



Nuculites are usually found. Ordovicic-Devonic. 



80. N. planulatus (Conrad). Ordovicic. 



Differs from N. neglectus in its smaller size, more prominent 

 umbonal ridge extending from the beak to the posterior extremity, 

 and in the conspicuous flattening of the shell hingeward from this 

 ridge. 



This species is the type of Hall's genus Cleidophovus founded 

 upon the fact that no hinge teeth had been ob- 

 served and also because of the flattening of the 

 shell just noted. 



Lorraine : New York, Pennsylvania. Utica : 

 New York. 



Fig. 508. Nuculites 

 (Clidophorus) neg- 

 lectus. a, b, exter- 

 nal views ; c, inter- 

 nal mold, enlarged. 

 (Minn. Surv.) 



81. N. neglectus Hall. (Fig. 508, a-c.) 



Ordovicic. 

 Differs from N. oblongatus in its smaller size 

 and in its subequal anterior and posterior ex- 

 tremities. 



