CRETACEOUS FOSSILS. 140 



wliile the anterior voutral region is ubrn})tlY cnneat.e; anterior margin 

 rounded in outline; base with a shallow seniiovate outline, being usually 

 slightly more prominent in advance of the middle; posterior margin long, 

 and very obliquely truncated, with a slightly convex outline, from the hinge 

 to the posterior basal extremity, Avhich is prominent and subangular; hinge- 

 margin very short, or little more than equaling one-third the length of the 

 valves; posterior umbonal slopes prominent, and more or less angular from 

 the beaks to the posterior basal angle; cardinal area short and rather nar- 

 row; beaks moderately prominent, incurved, and placed one-fourth to one- 

 third the length of the valves from the anterior margin. Surface ornamented 

 by moderately distinct lines of growth, crossed by obscure radiating costJTi 

 that are wider than the mere linear furrows between. 



I.ength, 1..50 inches; height, 1 inch; convexity, about 0.70 incli. 



1 only know this shell from casts that do not show the hinge. Th<!y 

 bear impressions, however, in some instances, of a ridge or projection along 

 the margin of the posterior muscular scar, as in Cuculhm. From the gen- 

 eral form of the shell, and its very short hinge-margin, I can scarcely doubt 

 that it belongs to Mr. Conrad's group Tr'ujonarca; but, until the hinge can 

 be seen, its relations to that genus cannot be satisfactorily determined. I 

 know of no very nearly allied species. 



Locality and j^ositmi. — East Canon Creek, Wasatch Range, Utah; in a 

 whitish sandstone of Cretaceous age. 



Genus AXINiEA, Poli. 

 AxiNiEA AVyomingensis, Meek 



Shell attaining a medium size, subcircular or vei-y slightly longer than 

 high, gibbous, thick, and strong; beaks rather prominent; Ijasal margin 

 semicircular, and rounding regularly upward in front into the anterior border, 

 which rounds to the cardinal edge, so as scarcely to produce more than a 

 very slight angularity at the connection of the two above; posterior margin 

 making a slightly broader and similar curve, excepting that it is faintly 

 sinuous above the middle; hinge plate thick, moderately arched, with denti- 

 cles rather strong, nearly straight, or a little curved, numbering about eight 

 or ten well-developed ones in front, and sev^n or eight behind, with per- 



