54 8 



NORTH AMERICAN INDEX FOSSILS. 



517. M. texana Roemer. (Fig. 750.) Comanchic. 



Right valve low, conical, with angular umbonal ridge; left valve 

 gently convex. 



Fredericksburg : Texas, Mexico. 



P'ig. 750. Monopleura texana; a, large valve from above; b, showing 

 both valves. (After Roemer. ) 



518. M. pinguiscula White. (Fig. 751, a, b.) Comanchic. 

 Right valve elongate. Radiating lines very much fainter than 



in M. marcida. Individuals apparently grew separately. 

 Upper Fredericksburg of Texas. 



519. M. marcida White. (Fig. 751, c, d.) Comanchic. 



Fig. 751. a, b, Monopleuyi pinguiscula ; c, d, M. marcida. (After White.) \ 



Surface of both valves covered with numerous raised radiating 

 lines besides the concentric growth lines. The individuals often 

 grew in clusters. 



Upper Fredericksburg of Texas. 



