27 St. Maurick and Claiborne Pelecypoda 27 



show, say at Burleson's Bluff, a vast range in surface markings 

 both as to number, strength and extent of ribs. In this respect 

 it resembles clarkeanns. It will be interesting to note in the 

 future the characteristics of the related types found in Louisiana 

 and Mississippi. 



7)'/)^.— Burleson Shell Bluff, C. U. Mus. 



Horizon. — St. Maurice Eocene. 



Specimens figured. — Fig. 11, loaned from U. S.Nat. Mus. 

 Figs. 12, 13, deposited in C. U. Paleont. Mus. 



Localites. — Burleson Shell Bluff, Collier's Ferry or Black 

 Bluff shoals and Smithville, Tex. 



Pecten cawcawensis, n. sp., PI. 16. Figs. 1-7' 



Specific characterization. — Size and outline as indicated by the 

 figures; surface ornamentation, — about 23 ribs on each valve, 

 broad with narrow interspaces on the right, narrower with wider 

 interspaces on the left ; rarely 'signs of intercostce on the right, 

 conuuon on the left ; imbricating, fine, concentric, lamellse more 

 pronounced on the right valve. 



This form has usually passed under the name of deshayesi, 

 but it will be seen by examining pis. 14 and 15 that the ribs of 

 ra-wcaicensis are much more sharply defined and differentiated and 

 lack the excessive ornamentation of superimposed riblets with 

 scaly imbrications in high relief. However, both are of the same 

 stock and doubtless will seem to intergrade when enough material 

 is collected from a large number of Mid-Eocene localities. 



Types. — Paleont. Mus., Cornell Univ. 



Horizoji. — vSt. Maurice Eocene. 



Localities. — Columbia Road, 17 mis N. of Orangeburg, S. C. 

 (not far from Cawcaw Swamp) ; Claiborne, Ala? (see pi. 13, 

 fig. 8). Above Newbern, Neuse River, N. C. 



Specimens from a locality numbered 5,205 in the U. S. Nat. 

 Mus. Catalogue (Flint River, old Danville Ferry, 16^ mis E. of 

 Americus, Ga. ) labelled deshayesi are more probably varieties of 

 eaivcazvensis. 



