460 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. 



He considered it difficult to sustain tins genus, or either of them, upon the 

 characters given, and referred all to the genus Conocephalites. 



Messrs. Hall and Whitfield, in describing Cambrian trilobites from 

 Utah and Nevada, discussed the genus Conocephalites and revived Crepi- 

 cephalus as a subgenus equivalent to Loganellus of Devine. They did not, 

 however, describe the genus Crepicephalus, but referred a number of species 

 to it which possess more or less distinctly marked "slipper- shaped" glabella?. 

 Professor Whitfield subsequently used the genus in his description of 

 Crepicephalus (Loganellus) montanensis ; x also in the Paleontology of the 

 Black Hills of Dakota. 2 But later (1882) he omitted reference to Loganellus 

 in describing Crepicephalus onustus? 



In 1884 I stated that Crepicephalus might be used as a subgenus of 

 Ptychoparia on account of its peculiar pygidium, but, from a recent study of 

 an entire specimen of the type species and of C. texanus, I think that we can 

 with propriety use it as a full generic term. The essential elements of the 

 head are generically identical with those of the head of Ptychoparia striata, 

 but the pleura of the thoracic segments and the pygidium vary in a marked 

 manner. The pleura terminates in the graceful backward-curving acu- 

 minate points so characteristic of many species of Paradoxides. This may 

 not be considered a character of generic value, but it gives a marked aspect 

 to the body of the trilobite in both C. iowensis and G. texanus. The pygidium 

 of C. iowensis is short, broad, and provided with two long- postero-lateral 

 spines which appear to be an extension of the border, but in reality are the 

 lateral extension of one of the segments of the pygidium. This feature is 

 more clearly shown in the pygidium of C texanus. The combination of 

 characters in the head, thorax, and pygidium clearly distinguishes the 

 genus from Ptychoparia and other genera of the Conocephalidse. 



Crepicephalus texanus Shumard sp. 

 PI. LXV, fig. 5. 



Arionellus (Bdthyurus) texanus Shumard, 1861: Am. Jour. Sci. and Arts, 2d series, 



Vol. XXXII, p. 218. 

 Arionellus tripunctatus Whitfield, 1876: Rept. Reconnaissance from Carroll, Montana 



Terr., on the Upper Missouri, to the l'ellowstone National Park (Ludlow), p. Ill 



PI. I, figs. 3-5. 



Numerous heads of this species occur in a dark-greenish-colored oolitic 



1 Bull. U. S. Geol. Sm-v. No. 30, p. 141. -Loc. cit., pp. 311-343. 3 Loc. cit., p. 182. 



