156 UNITED STATES GEOLOGICAL SURVEY OF THE TERRITORIES. 



to the lower part of the anal margin, (hough not angular; surface marked 

 by distinct lines of growth ; ligament narrow and depressed. 



Length, 1.70 inches; height, 1.34 inches; breadth, or convexity, 1.30 

 inches. 



This is a quite thick, strong shell, and will be readily recognized by its 

 oblique depressed Conn, its beaks and umbonal slopes ranging almost hori- 

 zontally. Its strongly-marked anterior adductor scars are ovate and oblique; 

 while the two little, disconnected, pedal scars above are very narrow, semi- 

 elliptical, and range obliquely backward and upward parallel to the margins 

 of the valves. The posterior muscular impressions are subcircular and very 

 shallow. 



None of the specimens show the entire hinge, but from fragments it 

 can be seen to be rather strong. The anterior lateral tooth of the left valve 

 is somewhat compressed and cross-striated One fragment shows the three 

 cardinal teeth of the right valve distinctly; they are very similar to those 

 of true Cyprina, excepting the larger size of the triangular pit between 

 the anterior two for the reception of the large tooth of the other valve. 



This species is evidently nearly related to the last, but it is much larger, 

 and not so distinctly truncated behind. Its anterior muscular impressions 

 are also deeper, and its anterior ventral region more cuneate. This latter 

 character is most observable in internal casts. 



Cyprina intermedia, d'Orbigny (Pakeont. France, III, 107, pi. 278, 



figs. 1-2), is also an allied form, but our shell is more depressed and oblique, 



and its posterior muscular impressions are located farther back, and differ in 



being nearly circular instead of elliptical; the beaks also appear to be more 



.prominent and pointed in casts than those of d'Orbigny's species. 



I place this shell doubtfully in the group Venilicardia, from its rounded 

 umbonal slopes and general dissimilarity in form to the typical section of 

 Veniella. So far as its hinge-characters have been made out, however, they 

 agree much better with the latter than with Venilicardia. Its pedal scars are 

 disconnected from those of the anterior adductors, thus differing from those 

 of Cyprina. 



Locality and position. — On a branch of Cheyenne River, near the Black 

 Hills; Fox Hills group, or No. 5 of the* Upper Missouri Cretaceous series; 

 also, in the very* upper beds of (lie same group on Cache La Poudre river, 

 in Colorado. 



