82 
Aug. F. Foerste 
Figs. 4, A, B, on plate IX of this Bulletin present posterior 
and lateral outlines of the type from the James collection which 
is illustrated by Fig. 1, / on plate IV. 
Strophomena elongata differs from typical examples of Stro- 
phomena planumhona chiefly in its greater width along the hinge- 
line and in its much greater convexity from front to rear. The 
shells frequently attain a width of 40 mm. along the hinge-line, 
and the posterodateral angles often reach 70 degrees. Not all 
the shells have acute posterodateral angles. Some specimens have 
considerable width compared with the length, but the angles at the 
hinge-line are almost rectangular. In some specimens the ratio 
of width to length is as seven to four. The specimens with acute 
posterodateral angles and with strongly convex brachial valves 
have a subtriangular appearance, but there is a tendency toward 
a flattening of the anterodateral slopes, the anterior outline re- 
maining more or less evenly rounded. The convexity from front 
to rear frequently equals half the length. In the original de- 
scription the shell is stated to narrow rapidly to the front, giving 
it a triangular outline. It is evident from the types that this 
statement is exaggerated and misleading. 
The muscular area of the pedicel valve is broadly oval. It 
is deeply impressed, the lateral borders are prominent and sharp, 
being deflected toward the front anteriorly, leaving a median 
gap. A low median ridge, sometimes bordered on each side by 
a narrow, linear area representing the adductors, divides the 
muscular area. On each side of this area the inner surface of the 
valve not infrequently is pitted or covered with low elongate 
papillae, usually interpreted as ovarian markings. The inner 
margin of the shell is thickened, especially anteriorly, and this 
thickening is crossed more or less radially by vascular markings, 
which may be traced a short distance toward the muscular area. 
Owing to the considerable convexity of the brachial valve, 
the interior surface appears deeply concave. The adductor mus- 
cle areas are deeply impressed posteriorly, and sometimes dis- 
tinctly limited also anteriorly, but usually several radial ridges, 
probably to be interpreted as vascular markings, cross the ante- 
rior outline. The two inner ridges of this set are extended 
anteriorly along the median part of the valve. The crural ridges 
are prominent and limit the adductor areas posteriorly. A broad 
ridge extends forward from the callosity anterior to the cardinal 
process. 
