24 Aug. F. Foerste 
Strophomena incurvata, Shepard^ 
XI 
{Plate XI, Figs. 7, 9 A, B, C) 
Brachial valve usually moderately convex, valves 40 mm. in 
diameter, having a convexity of 7 to 10 mm. Pedicel valve mod- 
erately concave, the concavity varying from 3 to 5 mm. in shells 
40 mm. in width. Postero-lateral angles usually varying between 
75 and 85 degrees, although occasionally the shell is sufficiently 
extended along the hinge-line to produce an angle of 60 degrees. 
The more quadratic forms are more common. In the specimens 
from Cloche Island, the shell frequently is wrinkled along the 
hinge-line. Usually these wrinkles are strongly oblique, making 
angles of 25 to 30 degrees with the hinge-line, although occasion- 
ally the angles are as low as 15 degrees, and still more rarely some 
of the wrinkles nearest the postero-lateral angles form angles as 
high as 60 degrees, resembling the more vertical wrinkles seen in 
Strophomena vetusta. Radiating striae on the brachial valve, 
usually about 7 or 8 in a width of 2 mm., where there is no inter- 
calation of additional striae. In those parts of the shell where 
numerous additional striae have been intercalated a short distance 
posteriorly, the number of radiating striae may reach 12 in a 
width of 2 mm. Striae usually subequal, or alternating in size. 
Occasionally, every fourth striation is more conspicuous, being 
stronger and more elevated. Striations transverse to the radi- 
ating striae, very fine. No evidence of concentric wrinkling. 
Hinge area on pedicel valve with a height of 3.5 mm. in speci- 
mens 40 mm. in width; decreasing in height slowly until near the 
postero-lateral angles. Margins of the delthyrium forming an 
angle of about 80 degrees. Deltidium low, frequently with the 
sides flattened so as to produce a more angular median line than 
is usual in other species of Strophomena. This angularity is 
best exhibited in the specimens from Cloche Island, but it is seen 
also in some of the Kentucky specimens. The more evenly con- 
vex deltidia also occur. The divergent sides of the deltidium 
extend diagonally forward from the median line for a distance 
of 5 or 6 mm. ; their distal terminations forming the dental plates. 
The latter extend from I to H mm. beyond the anterior margin of 
1 American Jour. Sci., vol. xxxiv, p. 144, 1838. 
