Strophomena and Other Fossils 
113 
equal striae in a width of 5 mm., or 7 or 8 stronger striae with 
enough intermediate narrower ones to give a total of 15 striae in 
this width. On the pedicel valve, the number of striae equals 
17 subequal in a width of 5 mm., or 15 stronger ones with suf- 
ficient finer ones to give a total 19 or 20 in the same width. 
There is no doubt that Strophomena planodorsata represents 
the western variant of Strophomena neglecta. Whether the species 
are to be regarded as essentially distinct must be determined 
from a much larger series of specimens than those which I have 
had the privilege of examining. Considering the distance 
between the area within which Strophomena planodorsata has 
been identified, and that in Indiana, Ohio, and adjacent Ken- 
tucky, within which Strophomena neglecta abounds, there is a 
probability of their being at least geographical variants, belong- 
ing to partially separated epicontinental oceanic basins. 
Strophomena fiuctuosa-occidentalis, nom. nov.^^ 
{Plate IX, Figs. 17 A, B, C, D; Plate X, Figs. 9 A, B, C, D, E) 
The species described by Winchell and Schuchert from Spring 
Valley, Minnesota, is a much smaller form than that figured by 
Billings under Strophomena fluctuosa, nor has it the greatly extended 
hinge-line. The wrinkles are concentric and are confined to the 
posterior flattened area of the valves ; they are more or less con- 
spicuously interrupted where they are crossed by the more prom- 
inent radiating striae. The latter alternate, at the geniculate 
deflection, with 7 to 11 much finer and quite inconspicuous striae. 
At the beginning of this deflection, the median one of the finer 
striae becomes conspicuous, and, farther down the slope of the 
deflection, the median striae of the secondary groups of finer 
striae become conspicuous in turn, especially along the median 
parts of the shell, so that along the border of the nasute part 
of the shell, and sometimes also laterally, there is an alternation 
of stronger striae with only one, two, or three finer ones. 
The most characteristic feature of the brachial valve is the 
relatively great height of its hinge-area, considering the small size 
of the shell. This height equals about 1 mm. in shells having a 
width of 20 mm. The posterior part usually is conspicuously 
Minnesota Paleontology, vol. iii, part 1, Plate XXXI, Figs. 14-17, 1893. 
