PREFACE. 



The following review of one of the Upper Cretaceous faunas as 

 developed in the interior region of the United States has grown out 

 of the study of a collection of fossils found by me in Huerfano park 

 and adjacent localities in southern Colorado. This collection, the 

 greater part of which was obtained during the summer of 1890, proved 

 to be especially interesting because it afforded data for the closer cor- 

 relation of certain Cretaceous strata in Utah with those east of the 

 mountains, besides adding a considerable number of new species to the 

 fauna of the Colorado formation. Dr. C. A. White, under whose direc- 

 tion the field work was done, generously assigned these fossils to me 

 for study with a view to publishing the results, and I am greatly in- 

 debted to his sympathetic aid in every phase of the work. 



The stratigraphic position of the Huerfano park fossils had been 

 fully established in the field to be beneath the Niobrara division of the 

 Colorado formation. In making the preliminary comparisons of spe- 

 cies it soon became evident that the fauna of this horizon was much 

 richer than had been supposed. Only about twenty-five or thirty 

 species of invertebrates had been definitely assigned to the strata 

 that are now included in the Colorado formation. Many had been 

 described simply as Cretaceous without assignment to more definite 

 horizons and a considerable number of other species had been erro- 

 neously referred to the overlying Montana formation. It therefore 

 became necessary to study as far as practicable the vertical range and 

 the faunal associates of these doubtful species, especially those re- 

 ported from Utah and New Mexico, making use of the collections of the 

 U. S. National Museum and of the Geological Survey, as well as the 

 published reports and my own observations in the field. This investi- 

 gation added a large number of species to the fauna of the Colorado 

 formation and showed the desirability of bringing together in one pub- 

 lication the scattered descriptions and illustrations of all the species 

 that can now be assigned to the fauna. While making this compila- 

 tion the nomenclature and descriptions of the species have been re- 

 vised in all cases in which better collections or other additional facts 

 seemed to make it necessary. Thirty-nine species are described that 

 are believed to be new to science. 



The purely paleontoiogic portion of the work is supplemented by a 



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