454 A. W. GRABAU PALEOZOIC DELTA DEPOSITS OF NORTH AMERICA 



either side of the rostral cavity and the strongly pnstnlose character of 

 the shell in this region. This is seen in the old age specimens from 

 Cincinnati, but appears to be the normal thing in this region. As a re- 

 sult, the internal molds always have a very strong projection in the beak 

 area. The brachial valve has a thick but short median septum, to which 

 are joined the converging crural plates. A small but distinct cardinal 

 process occurs. The radial plications ami concentric stria? are essentially 

 as in the Cincinnati specimens. A local variety might be made of this, 

 and the name ste :s proposed in recognition of the fact that our 



first knowledge of this region and of the fossils in this rock are du- tc 

 Prof. John J. Stevenson, who worked out much of the structure and 

 stratigraphy at a time when little was known of the Appalachians and 

 accurate maps were not available. 64 Stevenson reported from this lo- 

 cality Byssonychia radiata and Rhynchotrema capax. The former is well 

 represented, though the species is not radiata in the restricted sense. 

 The specimens identified as Rhynchonella capax are more doubtful. 

 Ulrich has identified them as Orihorhynchula linneyi. but a comparison 

 with typical specimens of the latter from Kentucky shows that this identi- 

 fication is at least as faulty as the other. The specimens have the char- 

 acter of a young Platystrophia and either represent the young of P. 

 stevensoni or a new species. 



The following is a complete list of the species identified from the 

 collections made in Walker Mountain : 



BRACHIOPODA 



Platystrophia lynx var. stevensoni var. nov.. abundant and of varying 



sizes. 



PELECYPODA 



1. hio walicerensis sp. nov. The common specie- of Byw - 



nychia in the Bays sandstone of Big Walker Mountain differs from B. 

 radiata. to which it has generally been referred, in the greater height of 

 the shell and the correspondingly shorter hinge line. Its most marked 

 characteristic is the sharp anterior flattening or impression, the limiting 

 angles of which are generally acute. The frontal portion thus outlined 

 is very pronounced, broad and marked by stronger radii than those on 

 the rest of the shell. The normal shell radii are flattened on the top 

 and separated by narrower interspaces. There are about 36 of the radial 

 plications. The height of a small specimen is 33 millimeters, the antero- 

 posterior length 14 millimeters, the thickness 17.5 millimeters. Another 



<-e his papers in the Proceedings of the American Philosophical Society, 1885; 

 vol. 22, 1S87. 



