stanton.] AMALTHEIDiE. 171 



Some representatives of Prionocyclus and Prionotropis, including 

 the types, were submitted to Prof. Alpliens Hyatt, and after examin- 

 ing tliem he states that they are generically distinct and that he also 

 regards both as separate from Schloenbachia properly restricted. I 

 shall therefore nse Prof. Meek's names. 



As to the genus Mortoniceras, the specimens from the Colorado for- 

 mation are hardly sufficient for generic determination and the original 

 description will be simply copied under the old names. 



Prionocyclus wyomingensis Meek. 



PI. xl, Figs. 1-4. 



Ammonites serratocarinatus Meek, 1871, Proc. Am. Philos. Soc., vol. XI, p. 429. 

 Ammonites (Pleuroceras f) serratocarinatus Meek, 1871, Aim. Rept. U.S. Geol. Sur. 



Terr, for 1870, p. 298. 

 Prionocyclus wyomingensis Meek, 1876, U. S. Geol. Sur. Terr., vol. IX, p. 452; White, 



1880, Ann. Rept. U. S. Geol. Sur. Terr, for 1878, p. 35, PI. 15, Figs, la-e; Whitfield, 



1880, Geol. Black Hills of Dak., p. 440, PL 14, Figs. 1-3. 

 Not Ammonites serratocarinatus Stoliczka, 1865, Cret. Cephalopoda of Southern 



India, p. 57, PI. 32, Fig. 3. 



Original description: 



"Shell attaining a rather large size; discoid, with periphery pro- 

 vided with a very narrow, prominent, serrated mesial keel, including 

 the siphuncle. Yolutions increasing rather gradually in size, some- 

 what compressed laterally, and a little excavated without being dis- 

 tinctly 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 costae, some of the larger of which bear a small, somewhat 

 elongated node near the umbilicus, and two closely approximated small 

 nodes around the ventro -lateral margins, where they all curve very 

 strongly forward as they pass upon the periphery; spaces between each 

 two of the large nodose costae occupied by from one to about three 

 smaller ones. Septa unknown." 



The costae are very irregular and vary considerably in strength on 

 different individuals, but they retain the same character through all 

 the stages of growth, excepting that the smaller intermediate ones al- 

 most disappear from the last whorl of very large specimens. Frequently 

 two costae spring from a single node near the umbilicus and sometimes 

 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 costae. 



The septum, as shown in the figure, has the same general character 

 as that of Prionotropis ivoolgari, the principal difference being in the 

 greater breadth of the first lateral lobe. 



