CONTEIBUTIONS TO PALEONTOLOGY. 



63 



nal process consists of a bifid projection, each division of wliicli is doubly 

 grooved upon its exterior face. The socket-plates are strong, and united to 

 the base of the cardinal process ; while from the origin of the latter pro- 

 ceeds a central median ridge, which is obsolete in some specimens. In these 

 characters, the dorsal valve presents but slight diiferences from Mr. Da- 

 vidson's illustrations of Streptorhynchus crenistria in the Monograph of 

 British Carboniferous Brachiopoda, Plate xxvii, f . 6 & 7.* 



Similar characters are found to exist in StropJiomena subplana of CoN- 

 RAD.t This species, in well-formed individuals, has both valves convex; 

 but the dorsal valve the more convex. The area of the ventral valve is but 

 little wider than that of the dorsal valve ; and while the foramen of the 

 latter is closed by a distinct deltidium, that of the ventral valve is but 

 partially, or, in some specimens, not at all covered. The cardinal process 

 of the dorsal valve consists of two short divisions, supported by short and 

 much elevated socket-plates ; and externally it is partially, or entirely, 

 covered and protected by the deltidium, which rises from the flat area of 

 the same valve, curving outwardly over the process, and, in some cases, 

 rising nearly as high as the latter. 



The existence of this deltidium on the dorsal valve is not confined to this 

 species of the genus ; and in one at least of the Carboniferous species, it 

 has a notch corresponding to the division of the cardinal process. This 

 feature, however, is not peculiar to Streptorhynchus, but occurs in 

 Strophomena rugosa and in S. alternata.X 



The following figures of S. subplana will serve to illustrate the characters 

 here noticed. 



Fig. 2. 



Fig. 1. Ventral valve of a large individual from Lockport, Niagara county. 



Fig. 2. Cardinal view of a specimen from Waldron, Indiana (enlarged) ; showing the deltidium 

 in the dorsal valve, while the foramen of the ventral valve remains open. In au 

 imperfect specimen from Lockport, the ventral foramen is partially closed. 



* See illustrations of S. woolworthana, Pal. N.Y., Vol.iii, pi. 17. 



t I have already indicated this species as belonging to the Genus Streptorhynchus, 

 in Geo], Report of Wisconsin, published January 1862; and in Transactions Albany 

 Institute, Vol.iv, April 1862, published May 1863. 



t The same feature, in a lesser degree, is also shown in the woodcut figure (1) of 

 Mr. Davidson, Monograph of British Permian Brachiopoda, p. 29 : Illustrations of 

 the Genus Streptorhynchus. 



