14 Ga On Sars: 
Seen laterally (fig. 1), the shell exhibits a rather regular, 
oblong elliptic form, the height scarcely exceeding 1/3 of the 
length. It is anything but equilateral, the umbones occurring 
far in front, at about the end of the first 5th part of the 
length of the shell. As usual, the umbones are somewhat 
prominent, and the edges of the valves in front of them 
appear suddenly deflexed. The dorsal margin behind the 
umbones is nearly straight and slightly declining, and joins 
the hind edge without any intervening angle. The ventral 
margin is gently curved, and quite continuous with the 
anterior and posterior edges, which both appear evenly 
rounded. 
Seen from above (fig. 2) the shell is found to be rather 
tumid, the greatest width almost attaining half the length, and 
occurring rather in front of the middle. Both extremities 
appear pointed, but the posterior one is much narrower 
than the anterior. 
The valves are of rather firm consistency, with the 
outer layer strongly chitinous, and are each provided with 
14 very conspicuous concentric lines, which form distinctly 
elevated ridges placed at rather regular distances from 
one another, the uppermost encircling the umbo. ‘These 
ridges represent the primary lines of growth, and are in all 
probability present in the same number in all fully adult 
specimens. On a closer inspection, they each exhibit in 
their posterior part a row of short and stout bristles (see 
fig. 3). The interspaces between the lines are closely and 
irregularly reticulated. On the other hand, the rather 
broad marginal area is quite devoid of such reticulation, but 
is marked by a great number of closely-set concentric striæ, 
which are not at all raised (see fig. 3) These striæ repre- 
sent the secondary lines of growth, and their number is 
OP iat 
