II St. Maurice and Claiborne Pelecypoda 



Conrad describes tlie one valve of this species as radians : Oblong, 

 compressed, lobed and flexuous on one side ; the ribs numerous, radiated ; 

 beaks very small, not prominent, pointed and a little curved laterally, 

 Vance's Ferry, S. C; Claiborne, Ala. 



O. sellcsformis : Oblong, convex, thick and ponderous, lobed; one 

 side of the larger valve profoundly sinuous and the opposite side gibbous ; 

 smaller valve sinuous and a little convex ; dorsal margin long and slightly 

 arched, with both extremities obtusely rounded. 



Since these are but different valves of the same species, Con- 

 rad's intimation that there are two valves of his sellc^forviis was 

 based on an error. This error, however, he corrected in 1S42, 

 strangely choosing sellccforviis instead of radia7is, a more appro- 

 priate name perhaps, and coming first in his original publication. 



As species are most generally defined in modern literature 

 several of the sellcpfornusASk& forms here included under one 

 name might be regarded as distinct species. 



With a small amount of material at hand, frorn a limited 

 number of localities, perhaps no one would hesitate to affirm that 

 verj' well defined species could be differentiated. But with the 

 increase of material from intermediate localities the seeming dis- 

 tinctness of certain tjq^es rapidh: disappears. Nevertheless there 

 is considerable fixity to some of these varietal forms and it is 

 well worth while to have them defined and named and have 

 their interrelations and stratigraphic significance pointed out. 



0. seliesformis var. smithvillensis, Plate S 



From Smithville, Tex., are derived numerous small speci- 

 mens with thin shells, and rareh', larger representatives, show- 

 ing one plicate valve and one nearly smooth valve, giving a 

 somewhat coinpressirostra appearance. Yet the plications are 

 very numerous and without the foliations and squamose charac- 

 ters of the latter species. The flat valve shows signs of weak pli- 

 cations. There is an entire lack of a marginal kink or fold — the 

 feature doubtless first suggesting the name sellcEf oralis. 



0. se!laeformis (tj-pical) Pis. 6 and 7. 



Rarely in Texas do the large, ponderous, saddle-formed mu- 

 tations of this species occur. From near Columbus on the Sabine, 



