PREFACE. 



This volume forms the third of the series deahng with the vertebrates 

 of the Permian or Permo-Carboniferous of North America. The author hopes 

 that the publication of these volumes has, in a large degree, cleared up the 

 synonymy and corrected the unavoidable errors of the earlier writers and 

 has laid a more secure foundation for the study of the primitive life of the 

 time. The object of the publication has not only been to describe the 

 morphology of the forms, but to prepare a basis for the study of their evolu- 

 tion and distribution, which will contribute to an understanding of the physi- 

 cal conditions and paleogeography of the closing portion of the Paleozoic. 

 The work will be continued on these lines. 



It is necessary, and most pleasant, to repeat my thanks to the Carnegie 

 Institution of Washington for the aid which has made the preparation of 

 these volumes possible; to the authorities of the American Museum of Nat- 

 ural History in New York, and to those of other institutions in this country 

 and Europe who have most generously placed material at my disposal. 



My thanks are especially due to Doctors Williston, Matthews, Broom, 

 and Broili for valuable advice and criticism; to Dr. Louis Hussakof, whose 

 contribution on the Fossil Fishes is an independent piece of work of the 

 greatest value; to Dr. E. H. Sellards, who has described two new fossil 

 cockroaches. 



Finally, I desire to thank Messrs. Christman and Thompson, of the Amer- 

 ican Museum, for the skill and care with which they have prepared many of 

 the drawings and photographs in this and the preceding monographs. 



E. C. Case. 

 November 30, 1910. 



