189 St. Maurice and Claiborne Pelecypoda 189 



smooth ; the strong concentric liration begins medially or basal- 

 ly, generally. But in rugosa it is the earliest stage of the left 

 valve that shows lirations, while below the shell is generally 

 smooth. It is also longish and has the aspect of the left valve of 

 the mufr/iiso7ii stock. The rotund, short, left valve of sniithvill- 

 cnsis is scarcely to be distinguished from the left valve of aldrichi. 

 The radiating lines of the latter species, however, are generally- 

 wanting. The illustrations on pi. 57 show these various charac- 

 ters. As already stated, gregorioi seems to be an inflated, nasute 

 alabamieyisis if Cossmann's figure is at all correct. 



The type of smithvillensis was rather unusually large and 

 smooth as published in the Proc. Phila. Acad., as noted above. 

 Corrugations are apt to cover a greater portion of the shell. 

 There is always something of an umbonal ridge, but in many 

 Louisiana specimens it is not at all prominent. Some remark- 

 ably large, senile, right valves of compressa have the outline and 

 superficial resemblance to dwarfed right valves of smithvillensis. 

 But the umbonal regions show marked differences : compressa 

 shows there a flattening, a well-defined concentric striation, and 

 a longish form approaching in characteristics its own left valve, 

 while smithvillensis is nearly smooth, nearly round, inflated, or 

 semispherical. Some older right valves of smithville7isis, if unus- 

 ually high and rugose, bear a striking resemblance to the Jack- 

 sonian wailesiana. One has only to glance at the respective 

 left valves to see that the two species are very far apart genet- 

 ically. 



Type. — Texas State Museum. 



Horizon. — St. Maurice Eocene. 



Speciviens figured. — Paleont. Mus. Cornell Univ. 



Localities. — Smithville, Bastrop Co. ; Burleson Shell Bluff 

 on Brazos River ; 2 miles E. of Alto, Cherokee Co., Mosley's 

 Ferry, Brazos River ; Cedar Creek, Wheelock League. Robert- 

 son C. ; Elm Creek, Robertson Co. ; Berryman's Land, Chero- 

 kee Co. ; Alum Bluff, Trinity River, Houston Co., 2 miles S. of 

 Mt. Selman P. O. ; i mile N. of Nevilles, Gonzales Co. ; 15 

 miles S. E. of Nacodoches, Nacodoches Co. ; Tex. Sabine 



