198 PALEONTOLOGY OF NEW YORK. 



Test thill, marked by concentric striiTJ, which, on the bod}' of the shell, 

 .are crowded into fascicles and assume a distinct regularity in passing over 

 the wing. The hinge shows one or two slender parallel grooves. 



Three similar specimens of the left have respectively the following 

 dimensions: length 32, 32 and 33 mm., hciglit 22. 2^") and 23 nun., and 

 hinge-line 25, 27 and 25 mm. 



In this species the l)ody of tlie shell resembles L. robustum and L. potens, but 

 is less oblique to the hinge-line, tln' wing less (U-lined. and its postci'ior 

 extremity not produced into a spine. 



Formation and locality. In the upper part of the Cheuuuig group, Lawrence- 

 ville, Tioga county. Pa. 



LkPTODKS.MA UMIiDNATUM. 

 I'L.VTK X.\n, FIG. 13; .VM> PL.iTE XC, KIG. 9. 



h^ptodesiiM uiiibonutiim, Hai.l. Pal. N. V., vol. v, \>\.\. Pliites ami Rxplanations : PI. 22, tig. 13. 



.Ian., 1883. 



Shell of medium size, rhomboidal ; body oblique, uainjuly ovate ; greatest length 

 one-half more than the height ; ante-byssal margin straight or slightly 

 convex, curving into the wide sinus, oblique below; ventral margin broadly 

 rounded ; posterior extremity moderately produced, abruptly recurved. 



Left valve convex, ventricose above the lower third. Right valve 

 unknown. 



Hinge-line straight ; length less than the length of the shell. 



Beak at al)out the anterioi' third of the cardinal line, directed slightly 

 forward, prominent and arching over the hinge. I'mltonal I'egion narrow 

 and ventricose, defineil anteriorly by a broad, shallow depression, which is 

 nearly vertical to the hinge-line, and posteriorly Ijy the abrupt depression of 

 the body. 



Anterior end acute, triangular. ^Ving rather large, triangular, convex, 

 joining the body of the .shell near the posterior extremity; margin bi'otidly 

 concave; extremity produced, acute. 



