I m; PALEONTOLOGY OF NEW YORK. 



and the basal margin and the striae along the posterior slope are not so abruptly 

 recurved. 



Formation and localities. In the Chemung group, near Corning, Chemung 

 county, and Portville, Alleghany county. X. Y. 



LePTODESMA DISPAK1LK. 

 PLATE -XXV. PIGS - I U«> PLATE LXXXIX. FIGS 



Leptodema disparile, llu.i.. Pal. N. ^ .. vol. v. pt. 1. Plates and Explanations: PL 25, figs. 2-4. 



Jan.. 1SS3. 



Shell of small or medium size, sub-rhomboidal : body ovate, oblique to the hinge 

 at about 4o°: length more than one-third greater than the height in the 

 left valve : ante-byssal margin oblique, gently curving into the sinus ; basal 

 and posterior margins regularly rounded. 



Left valve convex below, gibbous above. Right valve flai or concave 

 below, depressed-convex in the middle, and gibbous on the umbo. 



Hinge-line straight, greater than the length of the shell. 



Beak sub-anterior, prominent, rising above the hinge-line, directed slightly 

 forward. Umbonal region gibbous, subtending an acute angle. 



Anterior end large, somewhat produced, limited by a nearly vertical byssal 

 depression ; extremity obtusely angular. Wing somewhat large, joining the 

 body near the posterior extremity ; margin oblique below, concave above the 

 middle, and produced into an elongate spiniform process. The right valve is 

 smaller, the wing more extended and less defined, while the anterior end is 

 large and well defined by the byssal sinus and sulcus. 



Test marked by concentric, lamellose ridges with intermediate finer lines 

 of -row tb : the lamella- are sometimes more distinct on the right valve. 



Interior unknown. 



A left valve has a length of 28 mm., height 20 mm., hinge-line more than 

 -!o mm. A right valve has a length of 30 mm., height IS mm., home-line 



D DO 



33 mm. 



