LAMELLIBRANCHIATA. 273 



Hinge-line oblique ; length less than the height of the shell, merging into 

 the general curvature of the cardinal border. 



Beaks sub-anterior, appressed. Umbonal region moderately convex, not 

 gibbous. 



Test thick, marked by concentric laminae of growth. 



Anterior muscular impression close to the lower anterior margin. Pallial 

 line essentially parallel to the basal margin. Posterior muscular impression 

 large, situated upon the post-cardinal slope at some distance from the margin 

 of the valve. The internal mould shows strong radiating grooves from the 

 pallial line toward the basal margin. 



A large specimen has a length of 115 mm., and a height of 81 mm. A 

 somewhat smaller specimen has a length of 103 mm., a height of 71 mm., 

 and the depth of both valves, in the cast, is 24 mm. 



This species somewhat resembles M. maciknta, but is slightly more elongate, 

 much more regularly rounded posteriorly, the cardinal line more regularly and 

 broadly arched, the anterior extremity less produced, the beak more obtuse, and 

 the umbonal slope less defined. 



The specimen fig. 3, plate xli, was erroneously referred to M. perovata, in Pal. 

 N. Y., vol. V, pt. 1, Plates and Explanations, but clearly belongs to the present 

 species. 



Formation and localities. In the Corniferous limestone, six miles N.-W. of 

 Delaware, 0. ; and Babcock's Hill, Herkimer county, N. Y. 



MoDiOMORPiiA Clarens, n. sp. 



PLATE XLI, FIG. 4. 



Modiomorp/ia ptiomia (M. & W.), sp.. Hall. Pal. N. Y., vol. v, i)t. 1. Plates and Explanations : PI, 41, fig. 4. 

 Not Modiolopsm perovata, Mkkk & Wobthkn. Pi-oc. Acad. Nat. Sci., p. 246. 186."). 



t " " " Pal. Illinois, vol. iii, p. 438 ; pi. 11, fig. 2. 1868. 



Shell of medium size, ovate, sub-elliptical ; length nearly one-third greater 

 than the height; basal margin broadly curving (too straight in the figure); 

 posterior margin regularly rounded ; cardinal margin arcuate. Anterior end 



