206 PALEONTOLOGY OF NEW YORK. 



Wing joining the body near the post-extremity of the .shell, defined l>v a 

 shallow groove; margin oblique, straight, apparently slightly concave just 

 below the cardinal line. 



Tesl thin, Leaving upon the cast the marks of the stria' of growth which 

 have heen somewhat fascicled upon the body, giving it an ohscurelv undulated 



appearance. 



Interior unknot u. 



A specimen of this species has a length of 35 mm., height 24 mm., and 

 hinge-line nearly 24 mm. 



This species resembles L. Orodes, but differs in its greater obliquity ; the 

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



This one, and several other species, have shown the 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. 



PLATE XXV, FIGS. 0, '.i. (10?); vsi> IT.ATE XC, FIG. 3. 



Leptodesma Orodes, Hall. Pal. N. Y.. v.. I. v. pt. 1. Plates and Explanations: PI. 2.">. tip-s. 6,9(10?). 



.I:ui.. 1SS3. 



Shell of medium size, sub-rhomboidal ; body ovate, oblique to the hinge-line 

 at an angle of about 55°; length one-fifth greater than the height: ante- 

 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 becomes gibbous. Right valve 

 unknown. 



Hinge-line straight, a little less than the height of the valve. 



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

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

 angle of about :;o . 



