202 PALAEONTOLOGY OF NEW YORK. 



Anterior end small, terminating in a narrow nasute extension. Wing 

 comparatively large, triangular, joining the Ijody near the posterior end ; 

 surfiice concave ; margin gently sinuate ; extremity produced into a short 

 spiniform extension. 



Test thin, marked by line concentric .stria;, which are somewhat regularly 

 fasciculate on the body of the shell, crowded and sub-lamellose on the 

 anterior, and regular over the wing, curving backward just below the hinge, 

 indicating a spiniform extension of the wing. On the bod}- of the right 

 valve tlie striae form sharp, laiucllose elevations at somewhat equal intervals. 



Tlie hinge is marked In' one or two narrow, longitudinal grooves. 



A left valve has a length of 34 mm., height 24 mm., and hinge-line 22 mm. 

 A similar specimen, somewhat vertically compressed, has a length of 36 mm., 

 height 24 mm., hinge-line 25 mm. 



This species resembles L. vmbonatum var. depressum, but differs in its smaller 

 and narrower anterior end and more cyliniliicid body, ami wing without abroad 

 sinus in the margin. 



Formation and localities. In the upper beds of tlic Clienumg group, Steuben 

 county, N. Y., and Tioga and Bradford counties. Pa. 



Leptodesma Creon, n. sp. 



PLATE Xr, FIGS. U-i:!. 



Shell below medium size, sub-rlioniboidal ; liody ovate, oblique to the hinge- 

 line at an angle of about 5-3°; length nearly one-third gi'eater tlian the 

 height; ante-byssal margin slightly ol)li(|uc or rounded, distinctly sinuate 

 below, then gently curving to the broad l)ase; posterior margin broad, join- 

 ing the wing without interruption. 



Left valve convex below, giljbous above. Kight valve less gibbous than 

 the left and more expanded. 



Hinge-Une straight; length a little greater tlian the height of the shell. 



Beaks at about the anterior third of the hinge-line, sub-acute, directed 

 forward, prominent, arching over the hinge. Umbonal region very gibbous, 



