448 • DESCRIPTIONS OF NEW SPECIES OF FOSSILS FROM THE 



Formation and locality. Chemung group, near Warren, Warren county, PL-nn- 

 sylvania. 



LEPTODESMA PARALLELUM Simpson, n. sp., Fig. 14. 



Shell small, slightly oblique; body ovate; the basal margin frequently nearly 

 parallel with the hinge line; length usually a little more than twice the height; 

 t""^i_K'-~:s=n.-"-- anterior margin rounded; basal margin nearly straight, a little con- 



^^^. ' :j stricted anterior to the middle; abruptly recurving at the postei'O- 



fAlRs.'Tr.isas. basal extremity ; the posterior margin being obliquely truncate. 



Left valve convex, greatest convexity at the nmbonal region, becoming flattened 

 at the postero-basal portion. 



Right valve a little moi-e convex than the other but not gibbous. 



Hinge line straight, length about three-fourths that of the shell. 



Beak about one-fourth the length of the shell from the anterior end, prominent, 

 directed forward ; umbonal I'egion convex, descending much more abruptly on the 

 posterior than on the anterior side. 



Anterior end short, angular at the extremity, rounded below. A depression ex- 

 tends from near the beak to the basal margin a little anterior to the middle. Wing 

 very narrow, triangular, joining the body nearly at the posterior extremity ; margin 

 of wing straight, oblique ; extremity obtusely angular. The wing is distinctly sepa- 

 rated from the bodj^ 



Surface marked by concentric striae, which fiequently fasciculate on the anterior 

 portion of the shell. There are also concentric undulations. 



This species most closely resembles Leptodesma jyropinqiim, but the wing is more 

 distinctly separated fi-om the body, and the body is much less oblique, the basal 

 margin being sometimes nearly parallel with the hinge line; this latter feature will 

 serve to distinguish it from any other species at present known. When a little 

 covered by the rock it might easily be mistaken for some form of Sphenotus. 



Formation and locality. Chemung group, hill north of Warren, Warren county, 

 Pennsylvania. 



PTYCIIOPTERIA OBSOLETA Simpson, n. sp.. Fig. lo. 



Shell of medium size, subrhomboidal in outline; body ovate oblique, at an angle 

 of about forty degrees to the hinge line; height about three-fourths the length. 

 Anterior margin abruptly rounded ; basal margin curved outward at the extremities, 

 concave at the middle ; posterior margin somewhat abruptly' recurved. 



