303 
[Foerste. 
at the same distance from the beak ; and moreover the cardinal line 
of that species seems to be always less than the general width of 
the shell, while in the forms here described the cardinal line al- 
ways exceeds the general width of the shell. Moreover the flattened 
ventral valves of that species, with the moderately elevated beak 
are unknown in the Indiana collections so that this lends additional 
evidence in favor of the views here taken. Persons, not conversant 
with the manner in which many of our Clinton fossils of the lime- 
stones of Ohio and Indiana are preserved, would scarcely under- 
stand the difficulties attending such a usually simple problem as 
this. 
Strophomena corrugata, Conrad. 
(PLATE VI, FIG. 25.) 
Conrad’s type seems to have been a broad form similar to the 
second form of Hall, but to have had the coarser striae of Hall’s 
first form, as here designated. 
Strophomena corrugata , Conrad, as figured by Hall, consists of 
two forms ; one represented by Figs. 2, a, 6, c, the other by Figs. 
2, d , e, of PI. 21, Pal. N. Y. Vol. n. 
A single specimen of a ventral valve referred to the first form 
was found at Cumberland Gap, Tennessee. The valve is 18.7 mm. 
long and 20 mm. wide. It is moderately convex, rather flattened ; 
the sides are subparallel for about 13 mm. from the beak, the an- 
terior margin is semi-circular, the postero-lateral angles are slightly 
produced and slight corrugations, poorly defined, are noticed along 
the hinge line. The surface is ornamented with radiating striae, 
about seven in a width of 2 mm. The striae are distinct and large, 
with fine and less distinct striae intercalated in alternate order. 
The second form, found in New York, differs from the first chiefly 
in the relatively shorter length and corresponding increased breadth 
of the shell. There is also a difference in the character of the striae, 
which are usually finer, consisting of two to four fine striae inter- 
calated between eacn pair of somewhat coarser striations. This 
feature is not very conspicuous in the New York specimens ob- 
served, but in a form from Cumberland Gap it forms such a prom- 
inent feature as to suggest a separation from the species. 
Strophomena corrugata var. fluri-striata, var. nov. 
(plate VI, FIGS. 26, 27.) 
Shell broader than long ; the cardinal margin equal in width to 
