6Q University Geological Survey of Kansas. 



umbo, thence rounding over to the front, being usually some- 

 what flattened over the central and anterior regions, but with- 

 out any mesial sinus ; beak strongly incurved, and with its 

 most prominent part sometimes projecting a little beyond the 

 hinge line, but in others flattened, and with its immediate 

 apex nearly always terminating at the margin of the hinge ; 

 posterior lateral margins laterally compressed and converging 

 toward the umbo at nearly a right angle ; surface ornamented 

 by about ten to thirteen large, radiating, more or less angular, 

 simple or rarely bifurcating plications, which are themselves 

 (as well as the furrows between) marked by fine but distinct 

 radiating striae, which, toward the front, instead of continuing 

 parallel to the furrows and plications, converge forward on each 

 side of the latter so as to intersect along the crests of the same 

 at acute angles. Crossing all of these, there are usually toward 

 the front and lateral margins a few strong zigzag marks of 

 growth. Ventral valve more convex than the other, the great- 

 est convexity being at or near the beak, which is elevated and 

 usually more or less distorted, being sometimes twisted to one 

 side, and in other examples straight or somewhat arched back- 

 ward ; cardinal area narrow transversely, but proportionally 

 high, being often distinctly higher than wide, but well defined, 

 and usually finely striated transversely and vertically, either 

 flat or more or less arched backwards ; false deltidium closing 

 the fissure, narrow, and provided with a slender, rounded, 

 prominent mesial ridge extending to the apex of the beak ; sur- 

 face as in the other valve." The two dental lamellae of the 

 pedicle valve extend from the apex of the beak to the hinge 

 and forward about half the distance to the front of the shell, 

 dividing the beak into three nearly equal compartments. The 

 cardinal process of the brachial valve is curved forward and 

 upward, long, and thickened at the extremity. Measurements 

 of average specimen : Length, 23 mm. ; width, 29 mm. ; convex- 

 ity, 18 mm. ; length of hinge, 14 mm. ; height of cardinal area, 

 9 mm. 



Range and distribution : Upper and Lower Coal Measures ; 

 Fort Scott, Olathe, Kansas City, Eudora, Lawrence, Lecomp- 



