338 
PALEONTOLOGY OF NEW YORK. 
more or less divergent marks of the impressions of the lateral sliding muscles. 
The middle portion of the thickened margin slopes to the center of the shell, 
forming in the larger valve a line concave as to the beak, and in the smaller 
valve a sinus. The lateral portions of the thickened area merge gradually into 
the thin margins of the valves. Beneath the hinge-line in both valves is a 
narrow median septum, fainter in the small valve, and in both a scarcely visible 
ridge discernible only in oblique light. On either side of the septum begins a 
furrow which increases in depth and passes through the thickened area in a line 
parallel to the margins of the shell. 
“ The impressions of the vascular trunks of the mantle are continued from 
these furrows into the anterior portions of the valves and parallel to their 
margins. Secondary vascular sinuses radiate in great numbers from the main 
trunks toward the margins and center of the shell. 
“ In the median line of the larger valve, between the median septum and the 
anterior margin of the thickened cardinal region, lies a deep cordate pit, having 
its apex directed toward the anterior margin of the shell and with a shallow 
median furrow. In the sinus of the smaller valve is a faint median swelling, 
extending beyond the center of the shell and divided longitudinally by an 
obscure groove. 
“ Muscular impressions in five pairs for each valve; two of the adductors and 
three of the sliding muscles. The impressions of the adductors lying directly 
beneath the cardinal margin, are separated in the larger valve and in juxtapo¬ 
sition in the smaller. The anterior pair in the larger valve lies on either side 
of the cordate pit, in the smaller at the apex of the corneous callosity, extending 
into the middle of the valve and forming the sinus. Of the sliding muscles 
there is a pair on each side of both valves, close to the cardinal margin and 
between the lateral furrows and the margins of the shell. In the larger valve 
these scars are in juxtaposition, but in the smaller they are further apart, 
touching only at their extremities. The third pair of these impressions in 
the larger valve lies close against, but outside the anterior adductors; in 
the smaller valve on either side of the anterior extremity of the median 
swelling, in the sinus, and nearer together than the scars of the anterior ad¬ 
ductors. The scars of the paries passes closely about the muscular impres¬ 
sions, crossing both lateral furrows and terminating in the central portion of 
the cardinal margin.” 
