534 NORTH AMERICAN INDEX FOSSILS. 



478. P.? albequtte Beede. (Fig. 726.) Permic. 

 Surface marked with two to six faint ribs extending from the 



beak to the posterior margin ; growth lines strongest on anterior 

 portion of shell. Differs from P. occidentalis in being larger, and 

 in having an arcuate hinge ; from P. oblongus in being proportion- 

 ally much longer and in possessing radiating ridges. 



Very abundant in the upper Permic of Oklahoma (Whitehorse) 

 and Texas (Quartermaster). 



CXXXII. Cypricardella Hall. (Microdon Hall.) 



Equivalve, inequilateral, subquadrate, with straight or nearly 

 straight hinge line. Anterior end narrow and rounded. Posterior 

 end longer, broad, and truncate. Beaks small, appressed. Um- 

 bonal ridge more or less defined, extending backward from the 

 beaks. Surface marked with more or less lamellose concentric 

 striae. Hinge with a triangular tooth in each valve and corre- 

 sponding sockets. There is also in the right valve a longer trian- 

 gular fold or lateral tooth. Ligament external, extending nearly 

 or quite the whole length of the hinge line. Pallial line simple. 

 Devonic and Mississippic. 



479. C. tenuistriata Hall. (Fig. 727, a, b.) Devonic. 



Fig. 727. a, b, Cypricardella tenuistriata, left valve, and cardinal jview of small 

 specimen; c, d, C. bellislriata. (Pal. N. Y., V.) 



Larger than C. bellistviata with less angular umbonal slope and 

 less well-defined striae. 

 Hamilton : New York. 



