176 PALEONTOLOGY OF NEW YORK. 



Test thin, marked by line, closely arranged, concentric strke, which are 

 more crowded anteriorly; these arc crossed by extremely fine radii, which 

 arc chiefly confined to the shallow sulcus, anterior to the heak, and are also 

 obscurely marked on the wing. 



Ligamental area marked by two strong grooves. Two oblique linear 

 depressions along the posterior slope indicate the probable existence of lat- 

 eral teeth. Other characters of the interior, unknown. 



The specimen has a length of 11 mm., height 7 mm., hinge-line 12 mm. 



This species hears some resemblance to several species in the Chemung 

 group, but it is comparatively narrower and more oblique. 



Formation and locality. In the Marcellus shale, Bloomfield, Ontario county, 

 X. Y. 



Leptodesma Rogersi. 



['LATE XXI, FIGS 1 9. 

 Leptoilanna Rogersi, Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations: PI. 21, figs. 1-9. Jan., 1883. 



Shell of small or medium size, sub-rhomboidal ; body ovate, very oblique; 

 length greater than the height; anterior and basal margins broadly rounded ; 



posterior margin extended and abruptly recurved. 



Valves equally convex above. Right valve somewhat depressed below, 

 comparatively higher than the left. 



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



Beaks sub-anterior, obtuse, nearly erect, prominent. Umbonal region 

 gibbous, oblique. 



The anterior extremity is scarcely alate or auriculate, consisting of a. 

 rounded extension, straight above and slightly sinuate at the base. Wing 

 comparatively large, triangular, joining the body of the valve near the poste- 

 rior extremity, defined by the crowding and curving of the concentric stria?: 

 margin nearly straight for five-sixths of its extent, then acutely recurving; 

 extremity prolonged into a mucronate spine which extends beyond the poste- 

 rior limit of the valve. In the right valve the wing is less deeply sinuate. 



