Lamellibrajjchiata. 361 



convex below. Eight valve unknown. Hinge-line straight; length, 

 including the spine, nearly equal to the length of the valve. Beak 

 sub-anterior, obtuse, slightly oblique, prominent. Umbonal region 

 somewhat gibbous, subtending an acute angle. Anterior end 

 limited by a shallow byssal depression, acute and nasute at the ex- 

 tremity. Wing long, narrow-triangular, extending below the middle 

 of the valve ; margin sinuate ; extremity produced into a spine. 



Test thin, marked by fine concentric striae which are abruptly 

 arched on the posterior slope, regular upon the wing, and crowded 

 into fine irregular fascicles which are conspicuous on the anterior. 

 Some specimens show sharp, elevated, lamellose striae at equal dis- 

 tances on the surface of the body. The surface characters vary 

 with the different states of exfoliation and maceration. 



The largest specimen observed has a greatest length, from beak 

 to base, of 57 mm., height 36 nim., hinge-line, to base of spine, 35 

 mm. A small example of the left valve has a length of 34 mm., 

 height 18 mm., and hinge-line about 35 mm. 



This species is more elongate and oblique than L. longispinum, the 

 wing extends farther down along the posterior slope, and the anterior 

 extremity is fuller and more acute. 



Formation and localities. In the Chemung group at Panama, N. 

 Y. Other specimens from near Elmira, N. Y., and Mansfield, Tioga 

 county, Pa., are referred to this species with reservation. 



Leptodesma Matheri. 



Leptodesma Matheri, Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations : 

 PI. 22, figs. 8-10. Jan., 1883. 



Shell of medium size, rhomboidal ; body ovate, oblique at an angle 

 of 45° with the hinge-line ; length about one-half greater than the 

 height ; ante-byssal margin vertical in front, joining the broad cur- 

 vature of the byssal margin; posterior margin produced and abruptly 

 recurved. Left valve moderately convex below, scarcely gibbous 

 above. Eight valve shorter and less convex. Hinge-line straight ; 

 length much less than the length of the valve, but nearly equal to 

 the height. Beaks at about the anterior third of the hinge, obtuse, 

 directed slightly forward, not very prominent. Umbonal region 

 moderately gibbous, subtending an acute angle. Anterior end pro- 

 duced, flattened, acute at the extremity. Wing of moderate dimen- 

 sions, extending nearly to the posterior extremity ; margin gently 

 concave ; extremity produced and acute. 

 [Sen. Doc. No. 38.] 46 



