Strophomena and Other Fossils 
109 
or even posterior to the middle of the valve. The posterior part 
of the valve is distinctly flattened, and the part immediately 
anterior to the beak is slightly concave. The pedicel valve is 
rather deeply concave, although distinctly convex near the beak. 
These characteristics are possessed by the three specimens from 
the Eichmond group at Wilmington, Illinois, figured in this Bulle- 
tin, all from the Schuchert collection. The hinge-area of the 
pedicel valve is rather high and is approximately parallel to the 
flattened surface of the brachial valve. This feature is best seen 
when the shell is viewed from the side. The muscular area of the 
pedicel valve is subcircular. The limiting lateral ridges rise prom- 
inently above the body cavity; they are not strongly deflected 
toward the front anteriorly. Vascular markings extend radially 
toward the anterior margin of the valve. They are distinct even 
10 mm. back from this margin, and the shell is only moderately 
thickened within the area traversed by them. The radiating 
striae are about as fine as those of Strophomena planumhona, or 
slightly coarser. 
Compared with Strophomena concordensis, the brachial valve is 
more gibbous, the hinge-area of the pedicel valve is higher, and it 
is more nearly parallel to the flattened posterior part of the bra- 
chial valve. 
Strophomena planodorsata, Winched and Schuchert 
(Plate VII, Figs. 4 A, B; 6; 7 A, B; 8; Plate IX, Figs. 6 A, B; 7; 8 A, B; 9; 11; 12; 
14 A, B) 
The figures of the type, from the Eichmond group at Spring 
Valley, Minnesota, are reproduced as Figs. 6 A, E, on plate IX, 
of this Bulletin. The chief feature of this shell consists in its 
large size, subquadrate outline, and fine surface striation. The 
flatness of the brachial valve for more than half its length is very 
unusual in specimens of this large size and is well described by 
the term planodorsata. In a similar manner, the pedicel valve 
is only slightly concave for more than half its length, then curves 
up rapidly toward the anterior and lateral margins. 
Compared with this shell, the flattened area on the posterior 
half of the brachial valve of Strophomena neglecta certainly is less 
American Geologist, vol. ix, p. 286, 1892. 
