LAMELLIBRANCHIA TA. 
375 
Grammysia subarcuata. 
PLATE LXI, FIGS. 10-22; AND PLATE XCIXI, FIG. 26. 
Grammysia subarcuata, Hall. Prelim. Notice Lamellibranchiata, 2, p. 61. 1870. 
Grammysia (Leptodomus ?) subarcuata, Hall. Pal. N. Y., vol. v, pt. 1. Plates and Explanations: PI. 61, 
figs. 10-22. 1883. 
Shell of medium size, sub-ovate, widest at the posterior end; length more 
than one-third greater than the height; basal margin regularly convex, 
sometimes straight or constricted toward the anterior end. Posterior 
extremity rounded, or obtusely sub-angular, often sub-truncate above. Car¬ 
dinal line nearly straight. Anterior end short, abruptly rounded below the 
lunule. 
Valves moderately convex in the lower and posterior part, becoming gib¬ 
bous in the middle and umbonal region. 
Beaks sub-anterior, prominent, inclining forward and strongly incurved. 
Umbonal slope rounded. Post-cardinal slope flattened or concave, some¬ 
times limited by an elevation, at which line the concentric undulations ter¬ 
minate. Anterior to the middle of the shell, extending from the beak to 
the basal margin, there is a depression or cincture which often gives a slight 
undulation to the concentric folds and a constriction to the margin. 
Surface marked by fine, close concentric striae and by strong sub-angular 
concentric ridges or folds, which are frequently duplicate posterior to the 
cincture. The surface is also marked by fine, radiating, pustulose striae, 
which are often very conspicuous. Interior unknown. 
Three specimens measure respectively 36, 38 and 48 mm. in length, and 
20, 23 and 33 mm. in height. The largest specimen observed has a length 
of 70 mm. 
This species resembles G. arcuata in its general aspect, but differs in its more 
elongate form, more pointed posterior end, and the cincture is much more 
strongly marked. 
Formation and localities. In the arenaceous layers of the Chemung group, at 
Ithaca, near Elmira, Portville and Chemung, N. Y. 
