542 NORTH AMERICAN INDEX FOSSILS. 



503. C. halei Harris. Eocenic. 



No posterior umbonal slope present. 

 Lignitic : Georgia, Alabama. 



Fig. 741. Crassatellites gabbi, interior and exterior of the left valve and hinge, 

 enlarged. (After Harris. ) 



CXL. Etea Conrad. 

 Differs from Crassatellites in the absence of crenulations on the 

 inner free margins of the valves and in the hinge characters, pos- 

 sessing beside its two cardinal teeth, an elongate anterior and a 

 posterior lateral tooth in each valve ; anterior cardinal of left valve 

 triangular, fitting into a triangular pit of the right valve between 

 the two cardinal teeth of that valve. Cretacic. 



504. E. carolinensis Conrad. Cretacic. 

 Umbonal ridge subcarinate. Surface of shell marked with 



strong, more or less irregular concentric growth lines. 



Abundant in Ripleyan (Marshalltown) of New Jersey. Also in 

 North Carolina. 



505. E. trapezoidea (Conrad). Cretacic. 

 Less elongate than E. carolinensis and its posterior obliquely 



truncate margin is longer than in that species. 



Ripleyan of New Jersey (Merchantville), Alabama, Texas. 



CXLI. Ptychomya Agassiz. 



Like Crassatellites but with radial sculpture and with three 

 cardinal teeth in each valve, the posterior being very long and 

 double in the right valve, with resilifer in front. Comanchic- 

 Cretacic. 



506. P. ragsdalei (Cragin). (Figs. 742-743.) Comanchic. 

 Of medium size to large. Radial ribs in three systems which 



run at angles to one another. 



