LAMELLIBRANCHIA TA. 
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. macilenta, 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. 
Modiomorpha Clarens, n. sp. 
PLATE XLI, FIG. 4. 
Modiomorpha perovata (M. & W.), sp., Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations: PI. 41, fig. 4. 
Not Modiolopsis perovata, Mbek & Worthed. Proc. Acad. Nat. Sci., p. 246. lS6o. 
“ ? “ “ “ Pal. Illinois, vol. iii, p. 43S; pi. 11, fig’. 2. 1S6S. 
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 
