79 



We have only seen casts of this little shell, which do not 

 show the hinge sufficiently well to remove all doubts re- 

 specting its generic relations. In form and general appear- 

 ance, it is very similar to B. antiqu.a Munster, as figured by 

 Goldfuss, in Petrefact, pt. ii, p. 126, pi. cxvi, fig. 7 a-b, but 

 the posterior extremity of the hinge appears to be more 

 angular, and the sinus in the border of the antero-ventral 

 margin, is more distinct in our shell, the cardinal area also 

 appears to be generally narrower than that of B. antiqua. 



Locality. — Near mouth Smoky Hill fork of Kansas river, 

 Kansas territory. 



Leda (Nucula) subscitula. 



Shell subovate, a little gibbous in the central and umbon- 

 ial regions; posterior half more compressed and subros- 

 trate, very narrowly rounded at the extremity ; anterior 

 end elliptically rounded ; base forming a broad semiovate 

 curve, the most convex part of which is in advance of the 

 middle ; dorsum sloping slightly with a convex curve in 

 front of the beaks, concave and declining more gradually 

 behind ; hinge nearly straight, or sloping slightly from the 

 beaks, near which it is finely crenulate. Bea^s almost 

 central, rising somewhat above the hinge. Length 0*64 

 inch j height 0*23 inch ; breadth about 0*17 inch.. 



Our specimens of this species being merely casts of the 

 interior, and not showing the jpallial line, we are left in 

 some doubts as to whether it is a Nucula or Leda. 



In form it is very similar to our Nucula scitula* from the- 

 upper Cretaceous formations of the north-west, but the> 

 great difference in the geological positions of these two 

 shells, is alone a sufficient reason for regarding them as dis-- 

 tinct. 



* We have recently ascertained fro«a internal casta that our Jfi^c^ Evansi,, 

 and N. seitula, both have the palUal line sinuate,, and, consequently, "belong; 

 to the genus Leda, to. which we now refer them. 



