154 
PALEONTOLOGY OF NEW YORK. 
These strise become more conspicuous upon the margins and upon the wings, 
where they are often highly lamellose. The distant lamellae which mark 
the body of the shell are sometimes continued upon the hinge, and becoming 
stronger, curve over the margin, giving it a sharply annulated aspect, 
which, when preserved in the impression of the hinge-border, might be 
mistaken for a more important organic marking. Partially exfoliated shells 
show some obscure radiating lines which belong to the intimate shell-structure, 
and are not external. (These strise are too conspicuously represented in 
figure 6 of plate xii.) 
Posterior muscular impression situated near the middle of the posterior 
slope, and marked by irregular vascular striae ; from the lower anterior side of 
this impression the pallial line extends slightly downward, curving forward, 
and continuing in a line nearly parallel to the margin it terminates in a 
small muscular impression within the rostral cavity. The pallial line is 
frequently pitted or interrupted in its course, and from these pits radiating 
grooves extend toward the margin of the shell. 
Ligamental area extending the entire length of the hinge, comparatively 
wide, grooved longitudinally with fine, continuous parallel lines. Hinge with 
one or two linear, slightly oblique, lateral teeth on the posterior side, and 
with numerous erect or oblique irregular folds along the cardinal line below 
the ligamental area, which terminate on the inner margin in distinct crenu- 
lations. The cardinal wrinkles are smaller and more regular anteriorly, 
becoming large and irregular posterior to the beak. 
Three large specimens have the following respective dimensions: length 
90, 70, and 81 mm., height 100, 99, and 81 mm.; hinge-line 100, 90, and 90 
mm. An example of medium size has a length of 55 mm., height 76 mm., 
and hinge-line 48 mm. A large, erect individual measures 72 mm. in length, 
and 90 mm. in height. A small right valve has a length of 23 mm., height 
27 mm., and hinge-line 33 mm. 
This is an abundant species and attains a very large size in older individuals. 
In its different conditions of growth and preservation, it presents a very great 
variety of aspect, and it becomes extremely difficult to determine the limits 
