394 
THE PALEONTOLOGY OF MINNESOTA. 
[Stropboniena wiiicbeUi 
about as wide as long and distinctly limited laterally by linear elevations, with a 
depression outside of the latter; internally much thickened; apical perforation or 
pedicle opening exceedingly minute. Teeth not large for a shell of the size of this 
species; unsupported. Muscular depression very large, subquadrate in outline, with 
a sharply elevated outer margin, which has its postero-lateral limits outside the 
hinge teeth; medially divided by a more or less prominent ridge, upon each side of 
which are the large, longitudinally striated, diductor scars, enclosing the small 
adductors situated centrally in the posterior half. Space underneath the cardinal 
area filled up with shell matter. Near the outer margin there is occasionally a slight 
elevation, which is crossed medially by a few, not very prominent, vascular ridges. 
Entire interior surface covered with more or less radially arranged, delicate, oblique 
granules, which become more pronounced immediately outside the muscular margin. 
The size, large flattened area of the dorsal valve, and the subquadrate form of the 
muscular area of the ventr.al valve, distinguish this species from all others having 
the structure of S. rugosa. 
Formation and locality.— Rare in the Hudson River group near Spring Valley and Wykoff, Minnesota: 
Iron Ridge, Wisconsin, and Wilmington, Illinois. The interior characters are described from specimens 
from the last named locality. 
Collectors.— 'E. O. Ulrich, C. Schuchert. 
Mus. Reg. No. 8191. 
Strophomena winchelm Hall. 
PLATK XXXI. FIG. 11. 
1883. Streptorhynchus (Strophonella?) deltoidea Hall (not Leptatna deltoidea, 1847). Second Annual 
Report, N.Y. State Geologist, pi. xxxix, llgs. 10, 12-14 (not fig. 11 = 
-S. nutans.) 
1892. Strophomena winchelli Hall. Paia'ontology of New York, vol. viii, j)t. i. p. .144, pi. ix. 
figs. 10, 12-14; pi. XX, fig. 26. 
This species, though quite as large, differs from S. trentonensis in being more 
commonly longer than wide, and is probably the parent stock of the later appearing 
species S. nutans and S. fluduosa. From these it is separated readily by its thinner, 
less convex shell, finer and more numerous strise, the central disc also being without 
corrugations and less depressed than in S. nutans. A large collection would probably 
show intermediate variations between S. trentonensis and if?, winchelli, as are found to 
occur between S, rugosa and S. nutans of the Hudson River group. These transitional 
specimens are, however, rare and should therefore not be used to unite the species. 
If this were done, to be consistent, all the above mentioned forms, together with 
S. incurvata and S. neglecta should be referred to one common, widely distributed 
and variable species. 
Formation and locality.— Rave in the "Lower Blue beds" at Janesville and Clifton, Wisconsin. In 
the Galena at Oshkosh, Wisconsin. It has not been observed in Minnesota. 
Collector.— C. Schuchert. 
Mua. Reg. Nos. 8180, 8226. 
