MIOCENE MOLLUSCA AND CRUSTACEA. oo 
as differing from the normal type “in the greater elevation of the ears and 
the more distinct quadrangulation of the ribs of the convex valve.” As 
regards the elevation of the ears, they both appear to have the hinge line 
on a level with the point of the beak; and as to the extension laterally of 
the ears, I should judge from Mr. Conrad’s figures that they were closely 
similar; although I have never seen a complete valve from New Jersey, 
there are some with pertect ears, and I can see no important difference 
between these and the figures given by Mr. Conrad. The difference in the 
form of the ribs, if we can rely on Conrad’s figures, is quite a marked one, 
as the New Jersey specimens have the furrows deep and the edges 
extremely abrupt on the convex valves. 
The New Jersey examples seem to have attained a much larger size 
than those from Maryland. I have before me imperfect individuals which 
measure almost 3 inches across the ears, and of which the valves must have 
measured over 5 inches in width when perfect. The general form has been 
nearly equilateral and orbicular in outline, with large ears on each valve; 
one valve nearly flat or but slightly convex, the other moderately convex 
The flat valve has the ears depressed below the general level and a consid- 
erable space around or below the beak coneave and somewhat depressed, 
but not to a level of the surface of the ears. Each lateral margin forms a 
broad convex rib which is longitudinally striated; besides these, there are 
seven sharply elevated, prominent, and narrow ribs, a central one and three 
on each side; the surface of the ears is also obscurely radiated, while the 
entire surface is marked by fine, concentric, lamellose lines, strongly ele- 
vated. The convex valve has three broad very slightly convex ribs on each 
side of the central groove and a broad flattened space outside of these. 
The ears are slightly convex on their surfaces and are distinctly separated 
from the body of the shell by a depressed line. The right ear, when the 
shell is held with the convex side up, has a moderate constriction above the 
body of the shell, and the opposite one is very slightly extended along the 
shell in the same place. The entire surface of the valve, ears, lateral 
borders, and ribs is finely striated longitudinally and also concentrically, 
In the interior of the valves the ribs are profoundly marked, on the flat 
valve by deep narrow grooves and in the convex valve by broad rounded 
MON XXIV 3 
