320 JR. S. Lull — Mammals and Horned Dinosaurs. 



the stratigraphic sequence of the mammal-bearing beds. To 

 this end the Faculty of the Geological Department of Yale 

 voted a sum of money from the research fund which the 

 family of Professor James Dwight Dana have dedicated to his 

 memory. The brief visit, while not in itself productive of 

 many facts, nevertheless rendered possible a visualizing and 

 better appreciation of the work already done on the area and 

 stimulated the following compilation and summary of our 

 knowledge of the Cretaceous mammals. 



The sources of information are the large collections made 

 principally by J. JB. Hatcher, aided by Professor C. E: 

 Beecher, Mr. O. A. Peterson, and others, together with the 

 field notes and correspondence of the two first mentioned. 

 There were also available the writings of Professor Marsh 

 descriptive of the mammals themselves, and the subsequent 

 work of Messrs. Hatcher, Stanton and other authorities men- 

 tioned in the bibliography. 



I am indebted to Mr. O. A. Peterson of the Carnegie 

 Museum in Pittsburgh for aid in the compilation of localities, 

 as well as to Messrs. Gidley and Gilmore of the United States 

 National Museum ; and especially to Mr. J. T. Doneghy, Jr., 

 graduate student in paleontology at Yale, who shared the field 

 trip and prepared the geologic section of the Niobrara County 

 beds. Professor Schnchert's kindly criticism and generous 

 aid add to the already large sum of my debt of gratitude to 

 him. 



The Problem 



The late Cretaceous beds of Wyoming, which have received 

 from the United States Geological Survey the official designa- 

 tion of Lance formation, have borne at various times the 

 names of Laramie formation, Converse County beds, and Cera- 

 tops beds, all of which are open to criticism on one ground or 

 another. The strata are notable for having produced a large 

 number of most characteristic fossils, the skulls of horned 

 dinosaurs, in addition to other reptilian remains, but also for 

 having proved in certain localities a veritable mine of treasure 

 by the production of thousands of teeth and bones of the tiny 

 contemporaneous mammals. 



Whether such contemporaneity was exact, or whether the 

 mammals differed from the associated dinosaurs in level, facies 

 and implied habitat, and whether they occurred at more than 

 one level were aspects of my problem. If the latter proved 

 true, it would be interesting to learn whether or no a faunal 

 sequence exists in the mammals comparable to that which the 

 ceratopsian skulls seem to show, and what is the relationship 

 of the mammals to older and newer mammalian faunas. It 

 was hoped that more perfect, possibly associated skeletal 



