468 University . of Kansas Geological Survey. 



irregular branchlets and digitations ; first lateral lobe somewhat 

 longer than the siphonal and bipartite, with short irregular 

 branchlets and digitations occasionally in small specimens, with 

 the middle terminal branch proportionally broad, and so deeply 

 sinuous at the end as to impart more nearly the appearance of 

 a bipartite arrangement of the whole ; second lateral sinus nearly 

 resembling one of the divisions of the first, and in the adult with 

 merely a number of marginal digitations ; second lateral lobe a 

 little more than one -third as long, and from one-third to one- 

 half as wide as the first, generally tripartite at the end, but 

 sometimes in large specimens bipartite on one side of the shell, 

 the divisions being very short and simple, or serrated ; third 

 lateral sinus very small and merely bilobate, or in large speci- 

 mens digitate along the margins ; third lateral lobe hardly half 

 as long as the second, and in small specimens merely tridentate 

 at the end. 



" Largest specimen seen, seven inches in its greatest diame- 

 ter ; convexity, measuring between the costse at the larger, 

 broken end of the last turn, one and sixty-hundredths inches ; 

 convexity of the same, measuring so as to include the greatly ex- 

 panded costse, three and twenty-five-hundredths inches." 



Impressions of these shells occur abundantly in the Fort Ben- 

 ton limestone. They have been found in that horizon in Ells- 

 worth, Lincoln and Mitchell counties. 



Prionotropis Itt/attii Stanton. Plate en, figs. 5-8. 



Prinnotropis hyattii Stanton, 1892, Bull. U. S. Geol. Surv., p. 106, pi. xlii, 

 ff . 5-8. 



Stanton's description: "Shell of rather small size, com- 

 pressed discoidal, consisting of five or six whorls ; volutions 

 gradually increasing in size, embracing the earlier ones but 

 very slightly, so that the umbilicus is broad, though different 

 specimens vary somewhat in this respect. In very young ex- 

 amples the height of the whorls is greater than the breadth, 

 the keel is small, and more or less crenate, and the costse are 

 simple, lineate, and strongly curved forward at the outer ends, 

 without any nodes at first. L'sually every third or fourth costa 

 is stronger than the others. Some specimens three-fourths of 



