Notes on a Collection of Fossils. 193 



Orthoceras proiigenium Vamixem. This species is well 

 represented by two or three specimens, all showing the char- 

 acteristics by which it may be readily distinguished. See 

 works of Hall and Whitiieid already cited. 



Cyrtoceras luthei, n. sp. Shell rather small, elliptical 

 in transverse section, only moderately curved; length of an 

 average specimen from two and a half to three inches, great- 

 est diameter of body chamber three-fourths of an inch; septa 

 very numerous, ten chambers occupying the space of half an 

 inch; septa oblique to the axis, rising highest on the convex 

 side, the obliquity increasing as the septa approach the cham- 

 ber of habitation ; siphuncle large for the genus, situated close 

 to the inner or concave margin, tapering more rapidly in pro- 

 portion to size than the shell, and expanding to a trifling 

 extent between the septa. Outer chamber long; margin of 

 aperture and surface markings unknown. This species will 

 be readily recognized by its elliptical section, its oblique, 

 closely crowded septa, and its large, internal, rapidly tapering 

 siphuncle. 



The specific name is given in honor of Mr. F. H. Luthe, of 

 McGregor, Iowa, to whose skill and enthusiasm science is 

 indebted for valuable additions to our knowledge of the fauna 

 of the Lower Magnesian Limestone in the valley of the 

 Upper Mississippi. 



The collection contains fragments of other species that will 

 sometime, we hope, be represented b}' identifiable specimens. 



In general aspect this fauna resembles that of the Calcifer- 

 ous sand-rock about Lake Champlain. The identity of the 

 species in som^e cases and the close resemblance in others, 

 leaves little doubt as to the exact equivalency of the Lower 

 Magnesian Limestone of Iowa with the Calciferous series of 

 northeastern New York. 



Geological Labor-\tory, 



University of Iowa, 

 May 25, i8g2. 



