270 PALEONTOLOGY OF NEW YORK. 



A small specimen preserving both valves has a length of 53 mm., height 

 38 mm., and depth of both valves 13 mm. A large right valve has a length 

 of 80 mm., and a height of 36 mm. 



This species is distinguished by the comparatively great width of the valves, 

 the rounded ventral margins and the compressed form of the shell. It resem- 

 bles M. Clarens in general form, but the posterior end is not so regularly rounded, 

 and the valves are higher than in that species. In M. complanata the umbo is 

 more prominent, the anterior end narrower and rounded, the posterior end not 

 so regularly rounded, and the posterior muscular impression is farther within 

 the cavity of the valv«. 



Formation and locality. In the Schoharie grit, Schoharie, N. Y. 



MODIOMORPHA REGDLARIS, n. Sp. 

 PLATE XXXV, FIG. I'i. 



Shell above the medium size, elongate, sub-elliptical ; length less than twice 

 the height; anterior margin abruptly rounded; ventral margin broadly 

 curved; posterior margin regularly rounded. Anterior end somewhat 

 narrow. 



Valves depressed convex ; the point of greatest convexity being near the 

 middle of the length. 



Hinge-line longer than the height of the valve, very slightly oblique. 



Beaks depressed. Umbonal region moderately convex. 



Test marked by strong concentric lamina) of growth. Interior luiknown. 



A right valve has a length of nearly 70 mm., and a height of 40 mm. 



This species differs from M. Schoharie in its more elongate form, longer hinge- 

 line and more rounded anterior end. It somewhat resembles certain forms of 

 M. mytiloides, but the hinge is not so oblique as in that species, the anterior end 

 is broader, and the ventral margin is more regularly curving. 



Formation and locality. In the Schoharie grit, Schoharie, N. Y. 



