PELECYPODA—PRIONODESMA CEA , 



387 



38. P. inornata Ulrich. (Fig. 491.) Ordovicic. 

 Both ends regularly rounded. Surface marked only with 



obscure concentric striae, usually appearing almost smooth. 



Lorraine of Ohio. 



XVIII. Ch,enomya Meek. 



Thin, equivalve, inequilateral, longitudinally oblong or subcyl- 

 indrical. Anterior side rounded, closed ; posterior long, truncated 

 and gaping. Surface marked with radiating granules and with 

 concentric growth lines. Cardinal margin inflected as in Allorisma. 

 Teeth absent. Ligament external. Scars of anterior adductors 

 and pedal muscles connected. Pallial line with broad, shallow 

 sinus. Carbonic and Permic. 



39. C. leavenworthensis Meek and Hayden. (Fig. 492.) 



Carbonic and Permic. 

 Surface covered with growth lines and a few concentric undula- 



FiG. 492. Chcenomva leavenworthensis (Kan. Pal., VI/II.) 



lations which curve up abruptly behind, parallel to the truncated 

 posterior margin. Type of genus. 



Coal Measures of Illinois and Iowa to Colorado ; also Permic of 

 Kansas. 

 40. C. minnehaha Swallow. Carbonic and Permic. 



Smaller than preceding, with prominent posterior umbonal slope. 



Coal Measures of Iowa, Illinois, Missouri, Nebraska ; Permic of 

 Kansas. 



