368 Thirty-fifth Report on the State Museum. 



This species is quite unlike any here described. 

 Formation and locality. In the lower beds of the Chemung group 

 at the Inclined Plane, near Ithaca, N. Y. 



Leptodesma Cadmus. 



Leptodesma Cadmus, Hall. Pal. N. Y., vol. v, pt. 1. Unpublished. 



Shell of medium size, rhomboidal ; body oblique, narrowly ovate or 

 sub-cylindrical ; length nearly one-third greater than the height ; 

 ante-byssal margin somewhat vertically truncate, sloping below into 



i the broadly curving base; posterior margin abruptly curved. 

 Valves convex, gibbous above; the right valve smaller than the 

 left. Hinge-line straight, nearly equal to the height of the shell. 

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

 forward, prominent, arching over the cardinal line. Umbonal 



r region abruptly gibbous, subtending an acute angle. Anterior end 

 small, terminating in a narrow nasute extension. Wing compara- 

 tively large, triangular, joining the body near the posterior end ; 

 surface concave ; margin gently sinuate ; extremity produced into a 

 short spiniform extension. 



Test thin, marked by fine concentric strias, which are somewhat 

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

 lamellose on the anterior, and regular over the wing, curving back- 

 ward just below the hinge, indicating a spiniform extension of the 

 wing. On the body of the right valve the striae form sharp, lamel- 

 lose elevations at somewhat equal intervals. The hinge is marked 

 by 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. umbonatum var. depressum, but differs in 

 its smaller and narrower anterior end and more cylindrical body, 

 and wing without a broad sinus in the margin. 



Formation and localities. In the upper beds of the Chemung group, 

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



Leptodesma Creon". 



Leptodesma Creon, Hall. Pal. N. Y., vol. v, pt. 1. Unpublished. 



Shell below medium size, sub-rhomboidal ; body ovate, oblique to 

 the hinge-line at an angle of about 55°; length nearly one-third 

 greater than the height ; ante-byssal margin slightly oblique or 

 rounded, distinctly sinuate below, then gently curving to the broad 

 base ; posterior margin broad, joining the wing without interruption. 



