THE PALEONTOLOGY OF MINNESOTA. 



LStrophomena wincliclli. 



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 ventral 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. 



Mm. Beg. No. 8191. 



STROPHOMENA WINCHELLI Hall. 



PLATE XXXI, FIG. 11. 



1883. Streptorhynchus (Strophonella?) deltoidea HALL (not Leptcena deltoidea, 1847). Second Annual 



Report, N.Y. State Geologist, pi. xxxix, flgs. 10, 12-14 (not flg. 11= 

 S. nutans.) 



1892. Strophomena winehelli HALL. Palaeontology of New York, vol. viii, pt. i, p. 344, pi. ix, 



flgs. 10, 12-14; pi. xx, flg. 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. fluctuosa. From these it is separated readily by its thinner, 

 less convex shell, finer and more numerous striae, 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 S. winehelli, 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. Rare 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. 

 Must. Reg. Nos. 8180, 8226. 



