206 PALEONTOLOGY OF NEW YORK. 



Wing joining the })orly near the post-extremity of the shell, defined by a 

 shiillow groove; margin o()lifjnc. straiglit. apparently sliglitly concave just 

 below the cardinal line. 



Test thin, leaving upon tlie cast the marl<s of the striae of growth whicli 

 have been somewhat fascicled upon the body, giving it an obscurely undulated 

 appearance. 



Interior unknown. 



A specimen of tliis species Ims a leugtli oi' •")■") nini.. liciglit 24 nnn.. and 

 hinge-line nearly 24 nun. 



This species i-esembles L. Orodes, but dilTers in its greater obliquity ; the 

 bodv is more attenuate toward the anterior, and the wing is distinctly limited. 



This one, and several other species, have shown tlu' presence of an alar 

 furrow and obscure fold, similar to Ptychopteria. 



Formation and locality. In a coarse sandstone of the Upper Chemung group, 

 south of Smethport, McKean county, Pa. 



Leptodesma Orodes. 



l>r..\TE .K.\V, KIGS. B, 9, (10-); AND PLATE .XC, FIG. 8. 



Leptodesma Orodes, Hall. Pal. N. Y., vol. v. pt. 1. Plate.s iind Explanations: PI. 25, tip?. G, 9 (lOt). 



.Ian.. 1SS3. 



Shell of medium size, su])-rhomboidal ; body ovate, oblique to the hinge-line 

 at an angle of about 55°; length one-fifth greater than the lieight; antc- 

 byssal margin a little oblique, nearly vertical above, curving into a long, 

 undefined sinus ; ventral margin rounded into the broad posterior curve. 



Left valve moderately convex in the lower part, increasing in convexity 

 to the middle of the length, where it l)ecomes gibljous. Right valve 

 unknown. 



Hinge-line straight, a little less tlian tlie height of tlie valve. 



Beak sub-anterior, directed forward, moderately prominent, scarcely rising 

 above the cardinal line. Umbonal region abruptly gibljous, subtending an 

 angle of about 30°. 



