Weller — Kinderhook Faunal Studies. 121 



and is the only one which approaches perfection, even 

 remotely. Several other fragments are preserved in the 

 University of Michigan collection and labeled as this species, 

 but it is by no means certain that they are all the same. 



Cyrtoceras unicorne Win. 



PI. VII. f. 9. 



Shell arcuate, angle of divergence rapidly increasing with 

 the growth of the shell; transverse section laterally com- 

 pressed, oval in outline, narrowest along the side of least 

 curvature. Living chamber large, expanding towards the 

 margin; septa at distances of about 3^ mm., regularly con- 

 cave. Siphuncle apparently marginal along the side of least 

 curvature. Surface smooth except for some irregular lines 

 of growth near the aperture. In the type specimen the sep- 

 tate portion is 29 mm. in length and the living chamber 

 22 mm. ; the greatest diameter of the aperture is 40 mm. and 

 the shorter diameter 34 mm. ; at the first septum the longest 

 diameter, 24 mm., and at the seventh septum, the last one 

 perfectly preserved, the longest diameter is 16 mm. 



Remarks. There are several fragmentary specimens of 

 curved cephalopods in the University of Michigan collection, 

 all of which bear the label C. unicorne. The type specimen 

 here illustrated, however, is the only one sufficiently well 

 preserved to exhibit any of its essential characters. 



Agoniatites opimus (W. & W.). 



PL VII. f. 8. PL VIII. f. 1. PL IX. f. I. 



Goniatites opimus. Bull. U. S. G. S. No. 153 : 295. 



Shell large, discoid, gently convex on the sides, rather 

 sharply rounded upon the periphery. Number of volutions 

 not known, the inner ones embraced by the next outer ones 

 to a depth of one-half the diameter of the latter; the umbili- 

 cus rather small, but somewhat variable in size, being rela- 

 tively larger in the larger individuals, its sides rounded. 

 Aperture compressed crescentic in outline, the proportion of 

 height to width about as 7 to 5, the ventral margin sinuate as 

 indicated by the lines of growth. The size of the living 



