PELECYPODA—TELEODESMACEA. 



547 



515. R. patagiata White. (Fig. 749, d-f.) Comanchic. 



Both valves convex below and flat above, the peripheral angle 

 formed by the meeting of the upper and under sides is bordered in 

 the left valve by a thin, somewhat wrinkled carina. Beak of left 

 valve distorted by attachment. Right valve of more regular shape 



Fig. 749. a-c, Requienia texana, v ew of both valves and of the left and the 

 right ; d-f, R. patagiata, three views of a specimen with both valves together, X%- 

 (After White.) 



than the left. Surface of both valves marked by irregular con- 

 centric growth lines. 



Fredericksburg : Texas, Mexico. 

 516. R. texana Roemer. (Fig. 749, a-c.) Comanchic. 



Larger, thinner-shelled, than R. patagiata with less prominent 

 spires and without a prominent carina on the peripheral angle. 



Fredericksburg : Texas, Mexico. 



CXLVII. Monopleura Matheron. 

 Very inequivalve, smooth or ribbed, attached by right valve 

 which may be either twisted or coniform. Left valve conical 

 or flat. Dentition : two cardinals in free valve, and one in the 

 attached. Ligament external in a deep groove. Posterior adduc- 

 tor scar buttressed. Shell substance without canals. Shell often 

 found in groups adhering laterally. Comanchic. 



