464 University of Kansas Geological Survey. 



serrated, mesial keel, including the siphimcle. Volutions in- 

 creased rather gradually in size, somewhat compressed laterally, 

 and a little excavated without being distinctly channeled on 

 each side of the ventral keel ; inner ones but slightly embraced 

 by each succeeding turn, and consequently well exposed in the 

 wide umbilicus. Surface ornamented with numerous unequal 

 costse, some of the larger of which bear a small, somewhat 

 elongated node near the umbilicus, and two closely approxi- 

 mated, small nodes around the ventro-lateral margins, where 

 they all curve strongly forward as they pass upon the periphery ; 

 spaces between each two of the large nodose costse occupied by 

 from one to about three smaller ones. Septa unknown.'"' 



Stanton adds : " The costse are very irregular and vary con- 

 siderably in strength on different individuals, but they retain 

 the same characters throughout all the stages of growth, ex- 

 cepting that the smaller intermediate ones almost disappear 

 from the last whorl of very large specimens. Frequently two 

 costse spring from the same node near the umbilicus and some- 

 times are again united in the node near the periphery, but in 

 other cases they continue separate until they disappear near 

 the keel. Very few specimens show more than one row of 

 nodes near the periphery, and these are never developed into 

 spines. The serrations of the keel are small and somewhat 

 more numerous than the costse. The breadth of the whorl is 

 about two-thirds of the height in young specimens ; in larger 

 ones it is proportionately somewhat greater. The species some- 

 times reached a size of not less than twenty-five cm. in diame- 

 ter. The outer whorl of a specimen that is 125 mm. in diameter 

 measures thirty-eight mm. in width by forty-eight in height." 



Specimens from Septaria horizon, near Williams' Butte. 



Prionocyclus macombi Meek. Plate ci. 



Prionocyclus macombi Meek, 1876, Macomb's Expl. Exp., Geol. Rep , p. 132, 



pi. ii, ff. 3a-d. 

 Prionocyclus macombi Stanton, 1893, Bull. U. S. Geol. Surv. No. 106, p. 172, • 



pi. xli, ff. 1-5. 



Original description "Shell ^iscoidal ; umbilicus shallow; 

 somewhat less than the diameter of the last whorl from the 



