JbO PALEONTOLOGY OF NKIV YORK. 



and the basal margin and tin- stria' along the posterioi' slope are not so aljrujitly 

 recurved. 



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

 county, and Portville, Alleghan}- county, N. Y. 



Leptodesma disparile. 



I'l.ATE XXV, FIGS. 2-4 ; AXIi PLATE LXXXIX, FIGS. -23, 24. 



LejtlodesvM dliparile, Hall. Pal. N. Y., vol. v, pt. 1. Plates and Exjilanations : PI. 25, figs. 2-4. 



Jan., 1883. 



Shell of small or medium size, sub-rhomhoidal : Kody ovate, oblique to the hinge 

 at about 45°; length more than onc-tliird greater than the height in the 

 left valve; ante-byssal margin ohrKjue, gently curving into tlu' sinus; basal 

 and ])osterior margins regularly rounded. 



Left valve convex below, gibbous above. Right valve flat 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-antorior, 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 \ertical liyssal 

 depression ; extremity obtusely angular. Wing somewhat large. Joining the 

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

 middle, ami produced into an elongate spinit'orin judcess. The right valve is 

 smaller, the wing more extended and less dciiiu'd, while the anterior end is 

 large and well defined by the byssal sinus and sulcus. 



Test marked by concentric, lanicllose ridges with intei'mediate finer lines 

 of growth; the lamellae are sometimes more distinct on the right valve. 



Interior unknown. 



A left valve has a length of 28 mm., height 2U nun., hinge-line more tlian 

 30 mm. A right valve has a length of 30 mm., height 18 mm., hinge-line 

 33 mm. 



