iss I' ALvEONTOLOGY OF NEW YORK. 



\ specimen of a left valve has a length of I" nun., height 7.5 mm., hinge- 

 line about H) mm. A similar specimen has a length of 11 mm., height 6.5 

 mm., and hinge-line about I 1 mm. A right valve has a length of 9 nun.. 

 height 6 mm., hinge-line about 8 mm. Anotherone lias a length of 16 mm., 

 height 1 I mm., hinge-line about Iti mm . 



This is a small and abundant species, often occurring in great numbers mi 

 the surfaces of shaly layers. It is distinguished l>v its form and the regular 

 lamellose appearance of the surface. 



Formation mid localities. In the shales of the Chemung group at Connewango, 

 Cattaraugus county ; Nanticoke Springs. Broome county, and south of Ithaca, 

 N. Y. 



Leptodesma potens. 



PLATE \\I. FIGS 21, 30; PLATE WII. PIGS 11,12,19, 20?)21; v\i. PLATE I. XXXIX Hi. 7 



Leptodesma patens, Hall. Pal. N. Y., vol. v. pt. I. Plates and Explanations: PI. 21, figs. 21, :>o ; pi. 22, 



figs. II. 12, 19, 21. Jan.. 1883. 



Shell large, sub-rhomboidal ; body ovate, oblique, broad below; length more 

 than one-third greater than the height : ante-hyssal margin sub-truncate, 

 erect, oblique below; basal margin broadly curving ; posterior margin broad, 

 extended and abruptly recurving at the upper extremity. 



I. eft valve convex, gibbous above; the greatest convexity at one-third the 

 height of the shell from the beak. Right valve almost equally convex, more 

 abruptly gibbous on the umbo, and comparatively shorter and wider. 



Hinge-line straight, about equal to the length of the shell. 



Beak sub-anterior, obtuse, erect, prominent, arching over the hinge. 

 QmbonaJ region gibbous, very prominent, limited anteriorly by a shallow 

 depression extending from a point anterior to the beak to the margin at one- 

 third the height <>f the shell helow the hinge-line: posteriorly limited by the 

 abrupt post-cardinal slope. [Tmbonal angle acute. 



Anterior extremity extended and angular. Wing large, triangular, joining 

 the l>od\ uear the posterior extremity, distinctly limited; margin broadlj 



