386 Thirty-fifth Report on the State Museum. 



Test marked by fine concentric striae which are regular on the 

 posterior part of the body and the wing, and very crowded and 

 fasciculate on the anterior. 



A large left valve has a length of 60 mm., height 37 mm., hinge- 

 line 62 mm. A slightly larger, imperfect specimen has been found, 

 the body of which, near the posterior extremity, has a greatest 

 width of from 25 to 28 mm., and measures from 12 to 14 mm. in 

 the narrow part between the beak and the byssal sinus. 



This species differs from L. Pelops in the longer and more erect 

 body, more attenuate anterior extremity, more extended wing and 

 deeper sinus in the margin . 



Formation and localities. In the middle beds of the Chemung group 

 at Charleston, and near Mansfield, Tioga county, Pa. 



Section d, patulata. 



Leptodesma flacctdum. 



Leptodes?na flaccidum, Hall. Pal. N. Y., vol. v, pt. 1. Unpublished. 



Shell of medium size, rhomboid-ovate, spatulate below ; body oblique 

 at an angle of about 45° to the hinge-line ; length about one-third 

 greater than the height ; ante-byssal margin subtruncate, oblique, 

 a little concave below, curving into the broad ventral margin ; 

 posterior margin abruptly rounded and recurved. Left valve 

 moderately convex in the middle, gibbous on the umbo, depressed- 

 convex in the lower part. Right valve unknown. Hinge-line 

 straight; length about equal to the height of the shell. Beak 

 obtuse, directed forward, moderately prominent, situated anterior to 

 the middle of the cardinal line. Umbonal region gibbous, sub- 

 tending an acute angle. Anterior end comparatively large, pro- 

 duced into a nasute extension. Wing small, narrow- triangular, 

 joining the body of the shell more than one-third the height above 

 the base; margin gently concave; extremity acute. 



Test thin, marked by fine regular striae of growth, which are 

 fasciculate on the umbo and lamellose at nearly equal intervals on 

 the lower part of the shell. The hinge is marked by a single slen- 

 der groove. 



A left valve has a length of 40 mm., height 27 mm., hinge-line 

 about 27 mm. 



This species resembles L. complanatum, but differs in its greater 

 proportional length, and the body is more depressed and extended 



