PREFACE. 



The present work includes a series of papers dealing with the Permo- 

 Carboniferous deposits of north-central New Mexico and their vertebrate 

 fauna, so far as known. By courtesy of the Carnegie Institution of Wash- 

 ington it is published as a part of the series (publications 55, 145, and 146) 

 by E. C. Case, dealing with the fauna of the Permian beds of North America. 

 It has seemed best to us to publish these results jointly in order, by mutual 

 study, to avoid as far as possible any errors, misunderstandings, or dis- 

 cussions in literature. The material in each case was studied by the author 

 whose name appears first in the caption and the description and figures were 

 then referred to the other author for careful criticism and discussion. Both 

 authors accept fully all responsibility for the contents of the different chap- 

 ters, except where dissenting or supplementary notes are attached, signed 

 by the individual author. In all bibliographical references to the contents 

 of this work the names of the authors should be given in the order in 

 which they appear over each chapter. 



The chapter by Mr. M. G. Mehl was prepared under the direction of 

 Dr. Williston and both he and Dr. Case accept responsibility for the state- 

 ments and figures. 



The material described was collected by a joint expedition headed by 

 Drs. Williston and Case in Rio Arriba County, New Mexico, in the summer 

 of 191 1. The beds had been previously explored by Mr. David Baldwin, 

 in 1878 and 1879, chiefly in the interest of Yale University. Mr. Paul C. 

 Miller, of the University of Chicago, was one of the party and Prof. F. v. 

 Huene, of the University of Tubingen, was our guest for a short time. 



Several of the forms known from New Mexico have been described in 

 part or wholly elsewhere and such descriptions are not repeated. References 

 to these articles are given in the list and bibliography of the fauna. 



E. C. Case. 

 S. W. Williston. 



