PREFACE 



A numVjer of years ago the writer beg-au his studies of American 

 Carboniferous amnionoids with the preparation of a report on Marine Fossils 

 from the Coal Measures of Arkansas for the geolojrical survey of Arkansas, 

 uu'ler the directorship of Prof. John C. Branner, State geologist. This 

 work has been continued uninteiTuptedly since then in connection with 

 the writer's studies in the cephalopods of the Trias. 



In the prosecution of these studies the writer has spent much time in 

 the iield in Arkansas and Texas, and has had access to the material collected 

 bv the geological surveys of those two States. 



The writer desires to make acknowledgment to the gentlemen named 

 liclow for courtesies in the loan of sjjecimens and for assistance in the 

 prosecution of tliis work: 



Dr. John C. Branner, of Leland Stanford Junior Universitj-, formerly 

 State geologist of Arkansas, for the opportunity of studying the collections 

 of Carboniferous cephalopods made by the geological survey of Arkansas. 



Dr. Stuart Weller, of the University of Chicago, for the opportunity 

 of studying the Gurley collection (the richest in the United States in 

 Carboniferous ammonoids), for tlie loan of specimens and drawings, and 

 for much valuable assistance. 



Prof. Alpheus Hyatt, for the lean of specimens and for valuable advice 

 and sug'o'estions 



Prof. Robert T. Jackson, of Harvard University, for the loan of 

 specimens. 



Mr. Charles Schuchert, of the U. S. National Museum, for the use of 

 specimens. 



Mes.srs. E. T. Durrble and W. F. Cummins, of the geological survey 

 of Texas, and Prof. F. W. Simonds, of the University of Texas, for the 

 opportunity of studying the collections of the geological survey and of the 

 university. 



Mr. G. A. Graham and Dr. Gant, of Graham, Tex., for the gift of 



valuable specimens. 



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