210 PALEONTOLOGY OF NEW YORK. 



This species resembles, in its general form, L. extenuatum, but the body is 

 narrower at the beak, the wing less extendeil, and the greatest concavity of the 

 margin is just below the cardinal line ; while in that species it is near the 

 middle : the anterior extremity is also less prolonged. 



Formation and locality. In the upper shales of the Chemung group near 

 Canton. Bradford county, Pa. 



Leptoi)esm.\ Clitus, n. sp. 



I'LATF. X( . Via Jl. 



Shell of medium size, narrowl}' sub-rhomboidal ; body elongate-ovate, ohli([UL' 

 to the hinge-line at an angle of about 30° ; length less than twice the height ; 

 ante-byssal margin very oblique ; ventral margin broadly rounded, somewhat 

 abruptly recurved at the post-basal extremity. 



Left valve depressed-convex below, convex above, moderately gibbous on 

 the umbo. Right valve unknown. 



Hinge-line straight, less than the greatest length of the shell. 



Beak sub-anterior, directed forward, moderately prominent, rinbonal 

 region gibbous, subtending an acute angle. 



Anterior end narrow, prolonged into a rostrate extension, ileliued by a 

 strong byssal depression. Wing narrow-triangular, joining the body near 

 the posterior end, defined only by the abrupt recurving of the stride ; margin 

 deeply and abruptly concave, the deepest concavity about the middle ; the 

 extremity is an acute extension of the cardinal line. 



Test tliiii, marked by fine concentric stria;, \vhich are fasciculate iipdii tiic 

 l)ody, leaving the cast marked by gentle undulations, which are lamellose and 

 elevateil on the anterior side and rostral extension, and elevated on the wing. 



Interior unknown. 



A left valve has a length of M7 mm., hciglit ■_'<) nun., hinge-line '■'>'! mm. 



This species diflers from L. extenuatum in its lnoader l)ody, shorter hinge-line, 

 and narrower wing; the strioB bend more altruptly forward along the pnst- 

 cardinal slope, and the wing margin is more deeply concave. 



Formation and localities. In shales of the Chenunig grouji at Kelly's creek 

 and Mansfield, Tiosa countv. Pa. 



