536 Systematic Paleontology 



peculiarity lies in a ventral swelling which causes an apparent break in 

 the antero-median lobe. The ventral flange is unusually well developed 

 and the series of granules along the antero-ventral edge has not been 

 observed in any other species of the genus. 



Length 1.05 mm. ; height .G5 mm. 



Occurrence. — Helderbekg Formation, Keyser Member. Cumber- 

 land. 



Collection.- — U. S. Xational Museum. 



Family THLIPSURIDAE 



Genus THLIPSURA Jones and Holl 



TlILIPSURA multipunctata n. sp. 



Plate XCVIII, Fig. S 



Description. — -Valve subovate, tapering posteriorly, the ventral side 

 straight, the dorsal side strongly convex, the curvature of same semi- 

 circular in the anterior half, but growing less posteriorly ; surface mod- 

 erately convex, marked in the anterior half of the shell by a group of four 

 subquadrangular pits and with two, or rather three, elongated depressions 

 paralleling the post-dorsal half. 



Length of right valve 1.0 mm. ; width 0.6 mm. 



There is no described American species with which this need be com- 

 pared, indeed, this is the first recognition of the genus Thlipsura in 

 America. However, eleven or more species and varieties have been de- 

 scribed from the Silurian of Europe, and of these, T. multipunctata is 

 most closely allied to Thlipsura plicata var. hipunctata Jones and Holl. 

 In the latter form the anterior pits are only two in number while the pos- 

 terior marking consists of a single sulcus. In other respects the valves are 

 quite similar and in future study with abundance of material, our Ameri- 

 can species may prove to be only a variety or form of T. plicata. 



Occwrrence. — Oriskany Formation, Shriver Member. 21st Bridge. 



Collection. — U. S. National Museum. 



