LAMELLIBRANCHIA TA. 
283 
Formation and locality. In the arenaceous shales of the Hamilton group, at 
East Worcester, Otsego county, N. Y., associated with characteristic Hamilton 
fossils. 
Modiomorpha subalata. 
PLATE XXXV, FIGS. 6, 7 ; and PLATE XXXIX, FIGS. 1-14, 16. 
Cypricardites subalata, Conrad. Geol. Surv. N. Y., Ann. Rep., p. 83. 18414 
Modiomorpha subalata (Conrad), Hall. Prelim. Notice Lamellibranchiata, 2, p. 77. 1870. 
“ “ “ “ Pal. N. Y., vol. v, pt. 1. Plates and Explanations: PL 39, figs. 
1-14, 16. 1883. 
Shell of medium size or smaller, sub-quadrangular, or sub-ovate; sub-alate 
posteriorly, with the extremity obliquely truncate; length more than one- 
third greater than the height; basal margin straight or slightly concave on 
the anterior half, and thence regularly curving to the post-basal extremity; 
posterior margin abruptly recurved below, and continuing with a gentle 
curvature, or in a nearly straight line, to the cardinal margin; cardinal mar¬ 
gin oblique, nearly straight; post-cardinal area sub-alate. Anterior end 
short, abruptly rounded, often a little concave below the beaks, and limited 
by a more or less defined sinus, which extends from the beak to the basal 
margin, usually at a point less than one-third the length of the shell from 
the anterior end. 
Valves moderately convex below and in the posterior portion, more convex 
in the middle. 
Hinge-line oblique, about half the length of the shell. 
Beaks sub-anterior, incurved and directed forward, somewhat compressed. 
Umbo prominent, flattened anteriorly; the post-umbonal slope angular, gib¬ 
bous above and gradually declining to the post-basal extremity, which is 
sometimes obtusely angular. 
Test thin, marked by fine concentric striae, which are sometimes fascicu¬ 
late, forming distinct elevations upon the posterior slope, and often distinct 
angular striae upon the antero-basal portion of the shell, frequently becom¬ 
ing nearly obsolete on the umbonal region. 
Anterior muscular impression circular, of moderate strength; other interior 
characters undetermined. 
