392 Thirty -fifth Report on the State Museum. 



The striae are sub-lamellose on the anterior side, and sometimes 

 fasciculate on the wing. The fascicles on the body are often 

 marked on their summits by sharp, regular lamella?. The structure 

 as seen in exfoliated specimens is radiated ; but this does not appear 

 to be au exterior character. The hinge is marked by a single 

 narrow groove ; beyond this the characters of the interior are un- 

 known. 



A large left valve has a length of 45 mm., height 25 mm., hinge- 

 line 27 mm. A smaller specimen has a length of 28 mm., height 16 

 mm., hinge-line 17 mm. A right valve has a length of 26 mm., 

 height 15 mm., and hinge-line 15 mm. 



Formation and localities. In the Chemung group at Philipsburg, 

 Alleghany county, N. Y., and in Sullivan township, Tioga county, Pa. 



Leptodesma quadratum. 

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 Unpublished 



Shell of medium size, rhomboidal or sub-quadrate ; body ovate, 

 making an angle of nearly 40° with the cardinal line; length one- 

 third greater than the height ; ante-byssal margin nearly vertical in 

 front, rounding below into the shallow sinus, and extending nearly 

 the whole height of the valve ; ventral margin nearly straight ; 

 post-basal margin abruptly rounded and joining the wing without 

 limitation. Left valve convex, gibbous on the umbo, and obscurely 

 angular along the posterior slope. Right valve equally convex. 

 Hinge-line straight, equal to three-fourths the length' of the valve, 

 and equal to the height. Beaks situated at the anterior third of 

 the hinge, prominent and arching over the cardinal line. Umbonal 

 region gibbous, subtending an acute angle. Anterior end convex, 

 limited by a shallow, oblique, byssal depression which is nearly as 

 long as the height of the valve ; length one-half the height ; 

 extremity slightly produced. Wing triangular, scarcely defined, 

 joining the body at the posterior extremity ; margin oblique, straight 

 or slightly convex; extremity obtuse-angular. An imperfect right 

 valve presents about the same characters of wing. 



Test marked by fine striae of growth which are strongly fascicu- 

 late on the anterior end. 



A left valve has a greatest length of 31 mm., height 20 mm., and 

 hinge-line 21 mm. 



This species is distinguished by its short, broad, sub-quadrate form. 

 It has very much the aspect of Modiomorpha, but clearly belongs 



