144 PROCEEDINGS OF THE ACADEMY OP 



Cyprina compressa. 



Shell broad ovate, rather thin and compressed, somewhat narrowly rounded 

 at the extremities, base semi-oval ; beaks elevated, approximate, not strongly 

 curved, located about three-eighths the length of the shell back of the 

 anterior end ; cardinal border declining rather abruptly, with a greatly con- 

 vex outline, from the beaks towards the posterior end, concave and mere abrupt- 

 before the beaks ; surface unknown ; muscular impressions rather distinct. 

 Length 2.66 inches; height 2.1Y inches; breadth about 1.15. 



We are not sure we have seen specimens of this species showing the surface 

 characters; some fragments in the collection from the same locality and position 

 apparently of the same shell, are simply marked with rather strong lines of 

 growth. It is barely possible this may be a variety of the last ; the beaks, how- 

 ever, are so much more elevated, and farther removed from the anterior end, 

 that we are at present inclined to regard it as a distinct species. 



Locality and position. Same as last. 



Cyprina subtumida. 



Shell rather small, ovate, moderately gibbous ; anterior end narrowly round- 

 ed below the beaks ; posterior subtruncate at the extremity ; base forming a 

 gently convex curve, contracted towards the posterior ; cardinal border de- 

 clining with a long gentle curve from the beaks to the posterior end, concave 

 and very abrupt in front ; beaks located near the anterior end, directed ob- 

 liquely forward, not much elevated ; umbonial region gibbous ; valves prominent 

 or almost subangular from near the beaks obliquely backwards towards the lower 

 part of the posterior end ; muscular impressions not deep, anterior ones smaller 

 and more distinct than the others; surface unknown. Length (of cast) -92 

 inch ; height -65 inch ; breadth -55 inch. 



This species is not very nearly related to any we have seen figured in foreign 

 works, and may be known from any of those we have described from the North 

 West, excepting C. cordata, by its more gibbous form, more ventricose and 

 oblique umbonial slopes, as well as less elevated beaks. From C. cordata it 

 will be at once distinguished by its ovate form and greatly less elevated beaks. 



Our specimens do not show very satisfactorily the surface markings, as the 

 exterior has been mainly removed by the exfoliation of the shell. There are, 

 however, indications of lines of growth, and on the surfaces of the laminae 

 faint traces of radiating mai'ks ; though the latter may have had no connection 

 with surface markings. Not enough of the shell remains to show the character 

 of the points of the beaks. 



Locality and position. Yellow Stone River, in beds apparently a blending of 

 No. 4 and 5. 



Cyprina ovata. 



Shell ovate, compressed, rather thin, somewhat narrowly rounded at the 

 extremities ; base semi-ovate ; cardinal border declining with a gentle curve 

 from the beaks towards the posterior extremity, concave and sloping more 

 abruptly in front ; beaks not much elevated, rather small, approximate, not 

 strongly curved, located a little more than one-fourth the length of the 

 shell behind the anterior border; surface ornamented by distinct concentric 

 lines of growth ; lunule small, and not distinctly defined ; corselet lanceolate, 

 profound; hinge moderately thick, lateral teeth long ; cardinal teeth not very 

 prominent ; muscular and pallial impressions distinct, but not deep. Length 

 2-55 inches ; height 2-05 inches; breadth 1-15 inches. 



This species resembles C. oblonya, D'Orbigny, (Pal. Franc, torn. 3d, p. 105, 

 pi. 277, fig. 1-4,) but is more narrowly rounded at the extremities, and the 

 lateral tooth of the right valve is not near so prominent. 



Locality and position. Mouth Heart River, at junction of formation No. 5 of 

 the general section with the base of the Tertiary, but probably in the former. 



[May, 



