52 COLORADO FORMATION AND ITS INVERTEBRATE FAUNA. Ibull.106. 



characteristic species, such as Inoceramus labiatus, range from the bot- 

 tom to the top. The fauna as a whole may be regarded as the approxi- 

 mate taxonomic equivalent of the Turonian, though it is not probable 

 that either the beginning or the end of the epoch was contemporaneous 

 on the two continents. The few species that are compared with Ceno- 

 manian forms are not important. One of them, Nautilus elegans, occurs 

 in the upper part of the Colorado formation (at least in Texas), while 

 the Scaphites are associated with Inoceramus labiatus^ Prionotropis 

 woolgari, and Prionocyclus wyomingensis in the Fort Benton shales. 



The indefinite n ess of the correlation of the upper part of the formation — 

 the Niobrara and its equivalent, the Austin limestone — is shown by the 

 facts above given, the vertebrates belonging to the Turonian types, 

 while the mollnsks may be compared in part with Emscher or lowest 

 Senonian forms. As usual when an attempt is made to identify forma- 

 tions in such widely separated regions, the identification is most certain 

 when only one class of facts is examined, and becomes doubtful when 

 the facts are more numerous and are gathered from more varied sources. 



DESCRIPTION OF SPECIES. 



ECHINODERMATA. 

 CRINOIDEA. 



UINTACRINID^E. 



Genus TJINTACRINUS Grinneil. 



Uintacrinus socialis Grinnell. 



Uinfacrinm socialis Grinnell, 1876, Am. Jonr. Sci., vol. xn, p. 81; Meek, 1876, Bull. 

 U. S. Geol. Sur. Terr., vol. n, p. 375 ; Clark, 1893, Bull. U. S. Geol. Sur., No. 97, p. 21, 

 PI. 1, Figs, la-c, and PI. 2, Figs. la-e. 



This species and the following one having been recently described 

 and illustrated in a publication of the U. S. Geological Survey, are 

 listed here simply with references for the sake of completeness. 



ECH1NOIDEA. 



CASSIDULID^E. 



Genus CASSLDULUS Lamarck. 



Cassidulus stantoni Clark. , 



Cassidulns sfantoni Clark, 1891, Johns Hopkins University Circulars, No. 87, p. 76; 

 1892, Bull, U. S. Geol. Survey, No. 97, p. 73, PI. 35, Figs. 2a-d, 



