Strophomena and Other Fossils 85 
as that figured by Conrad and accompanying his unpublished 
manuscript. 
The type of Strophomena subtenta, numbered 922-2, is pre- 
served in the American Museum of Natural History, in New 
York City. It is a brachial valve, 19 mm. in length, 26 mm. in 
width, and 5 mm. in convexity. The concavity anterior to the 
beak is slight, and the flattening of the posterior parts of the 
valve scarcely extends farther than 11 mm. from the posterior 
margin of the shell. The divergent wrinkles along the hinge-line 
are distinctly defined. The postero-lateral angles of the shell are 
essentially rectangular, but rounded at the apices of the angles. 
The surface striae are subequal in size, and vary from 5 to 7 in 
a width of 2 mm. along the anterior margin of the shell, the first 
number being more nearly typical. Unfortunately the type 
specimen does not present the surface features of the pedicel 
valve, but other specimens show that the surface striae of the 
latter also are subequal in size, but are slightly finer than those 
in the brachial valve. 
A comparison of the type of Strophomena subtenta with those 
of Strophomena planumbona suggests that the former might be 
distinguished from the latter by the oblique wrinkling along the 
hinge-line and by the subequal surface striae. As a matter of 
fact, however, the oblique wrinkling is soon found, in the field, 
to be an individual characteristic, not uncommon in the individ- 
uals at some localities, for instance at Concord, Kentucky, 
but practically absent at other localities at the same horizon. 
In the same manner, the subequal size of the surface striae has 
been found to be an unreliable feature, specimens possessing these 
characteristics grading into others in which every third or fourth 
striation is more prominent. 
After having repeatedly seen the types of Strophomena plan- 
umbona and Strophomena subtenta, and having had them several 
times in my possession, owing to the courtesy of Professor Whit- 
field and Dr. Hovey, I spent several days at Clarksville, at Ore- 
gonia, and along the creek south of Jacksonburg, northwest of 
Trenton, Ohio, and elsewhere, localities at which it was possible 
to secure specimens from every foot of the section, in order to 
learn if it might not be possible to make at least some use of 
Strophomena subtenta as a variety characterizing some horizon, 
but without success. The best that can be said is that typical 
