stanton.] COMPARISON WITH MONTANA FAUNA. 47 



THE RELATIONS OF THE COLORADO FAUNA TO OTHER CRETA- 

 CEOUS FAUNAS. 



Within tlic geographic limits arbitrarily assigned to the Colorado 

 formation in the early part of this paper there is only one other marine 

 Upper Cretaceous fauna — that of the Montana formation* which imme- 

 diately overlies it. The larger part of it was described and illustrated 

 by Prof. Meek in his volume on Invertebrate Paleontology, 1 and many 

 additional species have been described by Dr. White, Prof. Whitfield, 

 and others. A comparison of these two successive faunas shows that 

 they are remarkably distinct although, as should be expected, they 

 have some species in common and others that are very closely related. 

 The species that are considered identical nearly all belong to genera 

 whose species are seldom sufficiently differentiated to be depended 

 upon in close geologic correlation. Those that seem to have passed up 

 from the Colorado to the Montana formation are not usually found as- 

 sociated with tlte typical Montana fauna, but the most of them occur 

 in that peculiar phase of it that was developed along the western 

 shore line. 



In the following list of common and closely related species in the 

 two formations the interrogation after a name indicates a doubt as to 

 the identity of closely related forms: 



Colorado formation. Montana formation. 



Ostrea soleniscus. O. soleniscus. 



Ostrea prudent ia. O. patina. 



Anomia propatoris? A. propatoris. 



Modiola nmltilinigera. M. multiliiiigera? 



Inoceramus simpsoni. I. simpsoni. 



Barbatia microncma. B, micronema? 



Nemodon sulcatinus. . ? N. sulcatinus. 



Lucina aubundata. L. subundata. 



Venielfa mortoni. V. humilis. 



Anatina lineata. A. lineata ? 



Corbnla aubtrigonalts. C. subtrigonalia. 



Lunatia concinna? L. concinna. 



Baculites asper. B. asper? 



Placenticeraa placenta. P. placenta. 



In addition to these the species of Neritina, Uulimella, Chemnitzia, 

 and Admetopsis, occurring in the Colorado formation in Utah, belong 

 to types that are also found in the higher beds of the same region. 



If we now compare the Colorado fauna with the fauna of the Eipley 

 formation of the southern United States, which is believed to be the 

 equivalent of the Montana formation, some additional resemblances are 

 seen. For example, the genera Trigonarca, Gyrodes, Bostellites, and 

 Pugnellus are present in both, and the first two are represented by 

 similar species, but none of the forms that can be considered character- 

 istic of the Colorado fauna are known in any of the more recent faunas. 



Before comparing our fauna with others believed to have been con- 



»U. S. £eol. Surv. Terr., Vol. ix, Pis. 10-39. 



