2GO 



posteriorly and sloping in the same direction ; sockei ridges short, crenu- 

 lated, oblique; rounded, low, wavy elevations just bej r ond the points and 

 in front of the socket ridges ; a small but rather deep pit immediately in 

 front of the cardinal process, from which extends a low mesial ridge to 

 about the middle of the shell forwards, where it fades out ; the concentric 

 wrinkles of the exterior show through slightly, and the radiating striae 

 plainly, with small, but distinct, radiating rows of papillae, which are 

 rather distant from each other, to the ridge, but crowded together on the 

 front slope and toward the lateral margins ; no muscular scars observed, 



" Width of a specimen of medium size, measuring from the points of 

 the hinge-line, 1 inches ; length about three-fourths of an inch." James, 

 1874. 



Occurrence. MARTINSBURG SHALE (Eden division). Jordans Knob, 

 one and one-half miles northeast of Fort Loudon, Pennsylvania. Eden 

 shale of the Ohio Valley. 



Collections. Maryland Geological Survey, U. S. National Museum. 



LEPTAENA TENUISTRIATA Sowerby var. 

 Plate XLIX, Fig. 2 



Leptaena tenuistriata Sowerby, 1839, in Murchison's Sil. Syst, vol. ii, 



p. 636, pi. xxii, fig. 2a. 

 Leptaena tenuistriata Foerste, 1910, Bull. Sci. Lab. Denison Univ., vol. xvi, 



p. 45, pi. v, fig. 9. 



Description. The particular ^forrn of Leptaena found in the Sinuites 

 bed of southern Pennsylvania is in general aspect quite like specimens 

 from a similar lower Trenton horizon in Tennessee identified by Foerste 

 as L. tenuistriata Sowerby. Direct comparison with typical British 

 specimens is necessary before the identity of the American form can be 

 determined with certainty. In the meantime it is believed best to record 

 the Sinuites zone species as a variety. 



Occurrence. MARTINSBURG SHALE (Sinuites bed). One mile south 

 of St. Thomas and other localities in southern Pennsylvania. 



Collection. U. S. National Museum. 



