446 University of Kansas Geological Survey. 



angular in large shells ; beak usually small and inconspicuous, 

 but sometimes more prominent and curved laterally, often 

 obscured by the scar of attachment, and by strong concentric 

 lines, and sometimes imbrications of growth. The plications 

 are usually simple, but occasionally they bifurcate. Upper 

 valve nearly flat or sometimes slightly concave, with an outline 

 similar to that of the other valve, except that it is t somewhat 

 more narrow along the hinge line. Its surface is smooth for 

 some distance around the beak and the plications toward the 

 margin are not so strongly developed as on the lower valve, 

 which it resembles in other respects. The muscular scars are 

 reniform and subcentral ; ligamental area varying greatly in 

 size and form, but never very large. Conrad's type ( lower 

 valve ) measures seventeen mm. from beak to base, fifteen mm. 

 in breadth, and five mm. in convexity, while the corresponding 

 measurements of Ostrea blackii, which is the largest variety of 

 the species, are sixty-eight, sixty-two and thirty-two mm., 

 respectively." 



The above species is found in Lincoln marble, but is not 

 abundant. Good specimens are difficult to obtain on account 

 of the extreme hardness of the matrix in which they are im- 

 bedded. They are usually found associated with sharks' teeth. 

 Only the smallest variety of this species has been found in the 

 Kansas rocks, and as it has been found in one horizon only, I 

 am inclined to think that that horizon is correlative with the 

 "brown calcareous sandstone" horizon of Colorado in which 

 the form 0. lugubris is so abundant. See Stanton, 1. c. 



Ostrea anceps, n. sp. Plate cxvu. 



Description : Shell elongate, moderately subovate, dorsal 

 margin straight ; ventral margin curved ; beak truncated by 

 mark of attachment ; surface of truncated portion marked by 

 parallel lines of indentation. Upper valve having an elongate, 

 subovate, internal cavity ; lower valve very capacious, hol- 

 lowed under truncated beak. Internal surface of shell smooth ; 

 exterior surface not entirely discernible in type specimen, but 

 appearing rugose at margins ; hinge moderately long ; lig- 



