Maryland Geological Survey 451 



the width, moderately convex in the middle and on the umbo: anterior 

 margin long, slightly concave above and curving to the base; posterior 

 margin below the sinus, somewhat abruptly curving into the broad rounded 

 basal margin : anterior wing small, trigonal, subacute, distinctly sepa- 

 rated by a sinus from the body of the shell ; posterior wings large, subacute 

 at the extremity, not strongly distinct from the body of the shell, extend- 

 ing as far as, or a little beyond, the margin of the shell ; marginal sinuosity 

 long and shallow. Surface marked by moderately strong radiating costge 

 and strong elevated concentric striae." Hall, 1859. 



To this species is referred a fragment which has the sculpture and out- 

 line, as far as this latter can be made out, of Hall's species. It is freely 

 admitted that such reference is a mere conjecture. 



Occurrence. — Oriskany Formation, Eidgely Me^iber. Cumberland. 



Collection. — George M. Boeder. 



[Ohern.] 



Genus LEPTODESMA Hall 



Leptodesma ? sp. 

 Plate LXXV, Fig. 3 



Description.- — Three incomplete internal casts whose outlines and other 

 characters cannot be made out with certainty are tentatively referred to 

 this genus. The ligamental area is long and wide and longitudinally 

 striated. Beneath the beaks are several fine transverse teeth, and posterior 

 to the beak is a hinge margin evidently corresponding to a tooth in the 

 shell. The anterior extremity seems to be neither nasute nor auriculate. 

 The anterior muscular impression is small and deep. In the cast the 

 position of pallial line is marked anteriorly by a sharp ridge. A part of 

 an exterior from the same rock mass shows the surface of the shell to be 

 marked only by irregular concentric growi;h lines. 



Length 5.5 cm. ; height 4.5 cm. 



Occurrence. — Ohiskany Formation, Eidgely Member. Eock Enon 

 Springs, Virginia. 



Collection. — U. S. National Museum. 



[Ohern.] 



