Strophomena and Other Fossils 
69 
The specimens represented by figures A, B, C, accompanying 
the original description, were 23 mm. wide and 21 mm. long. They 
have a sub-pent agonal outline. Anterior to a line drawn trans- 
versely across the center of the shell, the outline is broadly V- 
shaped, rounded at the anterior extremity. Posterior to this 
transverse line, the sides of the valve are only moderately diver- 
gent or nearly parallel. The posterior part of the brachial valve 
is flattened. From this flattened area, the shell is deflected 
strongly toward the anterior margin, especially toward the antero- 
lateral sides, producing a strongly convex, subnasute appearance, 
which suggested the term nutans. The pedicel valve is rather 
strongly concave, the maximum depression being about two- 
thirds of the length of the shell from the beak. The radiating 
striae are fine, every fourth one tending to be slightly more prom- 
inent. The muscular area of the pedicel valve is deeply im- 
pressed, and the border of this area rises sharply and prominently 
above the general surface. The interior of the valve is conspic- 
uously thickened along the border, the amount of this thickening 
being greatest near the middle of the anterior border, where it 
presents a very steep slope, having a height of almost 8 mm. above 
the general plane of the margin of the valve. This thickened 
border is crossed by strongly impressed grooves, called vascular 
markings, which are most conspicuous near the median parts 
of the border, where the latter attains the greatest elevation. 
Several ridges, limiting vascular grooves, extend posteriorly as 
far as the anterior border of the muscular area. The space 
betwnen the muscular area and the thickened border is marked 
by small ovarian pits. 
In other specimens of the same general appearance, the alter- 
nation of more prominent striae with sets of three finer striae 
is shown best by the pedicel valve, but a similar tendency is 
shown also along the postero-lateral angles of the brachial valve 
and over the flattened umbonal area. Anteriorly, on the deflected 
marginal portion, the striae are coarser, and either alternating- 
in size or approximately subequal. About 13 striae occupy a 
width of 5 mm. Some specimens are fully mature when they 
have reached a width of only 20 mm., while others attain a 
width of 25 mm., a length of 21 mm., and a convexity of 10 mm. 
The thickened border along the interior of the pedicel valve may 
reach a height of 10 mm., measured from the anterior margin of 
