SILURIAN SPECIES. 19 



although it shows nearly the same number of volutions. Its volutions are 

 also proportionally" more convex below, and slope more abruptly into the 

 umbilicus. 



Locality and position. — Same as last. 



Eaphistoma? TEOcniscus, Meek. 



Plate 1, figs. '.\, 3 a, and 3 h. 



Euomplxalus {Eaphistoma ?) trochiscus. Meek (1870), Proceed. Acad. Nat. Sci. Philad., 

 Gl ; and (1872) in Hayden's Aun. Eep. Geol. Survoy of the Territories, 4G4. 



Shell sublenticrjar, about twice and a half as wide as high; spire much 

 depressed, or but little higher (measuring from the horizon of the sharply 

 angular periphery) than the convexity of the last turn below the same; um- 

 bilicus wide, deep, and depressed-conical; volutions four and a half to five, 

 increasing gradually in size, all obliquely flattened (or sometimes slightly 

 concave) above, nearly on a line with the slope of the spire, and sloping 

 downward and inward below to the umbilicus, into which the curve is so 

 abrupt as to form an obtuse angle around its margin ; aperture wider than 

 high, and rhombic- subtrigonal in outline. Surface unknown. 



Breadth, 0.40 inch ; height, 0.15 inch ; breadth of last turn, 0.12 inch ; 

 breadth of umbilicus, about 0.25 inch. 



This is similar in general appearance to the last species, but may be 

 readily distinguished by its less numerous whorls, which increase more 

 rapidly in size. It is much more nearly allied to a form now before me in 

 masses of chert, from the west side of Lake Pepin, in Minnesota, found in 

 beds of about the age of the Calciferous sand-rock of the New York series. 

 The latter, however, attains a much larger size ; some of the specimens 

 being an inch in diameter, with about six volutions. The Minnesota form 

 is also more sharply angular on the periphery, and has the upper side of the 

 volutions distinctly more concave, and the spire more depressed.* 



Locality and position. — Same as last. 



* In the Proceedings of the Philadelphia Academy for 1870, cited above (p. ^2), I 

 have proposed the name E. Pepinensis for this Minnesota species. 



