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THE AMERICAN NATURALIST. [Vol. XXXV II. 



sion of the American Museum of Natural History in New York, 

 and through the kindness of the Director of the Department of 

 Paleontology the author was permitted to examine the types 

 during the past summer. As the material was made available 

 to me even before cataloging by the Museum, I desire to express 

 my thanks publicly to Dr. H. F. Osborn for his kindness in 

 the matter. 



Unfortunately the most of the type specimens have never 

 been freed from the matrix, Prof. Cope contenting himself with 

 the description of new forms and such characters as could be 

 made out from the uncleaned specimens. A reexamination of 

 the types in the light of better preserved and prepared material 

 has led me to conclusions very different from those of Cope and 

 of far-reaching effect upon the classification of the Pelycosauria 

 and the related Permian reptiles of other countries. 



These conclusions may be stated as follows : — 



1 . All known reptiles from the American Permian, other than 

 the Cotylosauria, possessed two temporal arches; there is no 

 approach to a single zygomatic arch, as described by Cope in 



2. The Pelycosauria followed a line of development that led to 

 extinction while the persistent line of development was followed 

 in other regions, perhaps in Africa. The progress of develop- 

 ment, from a stage represented b\ Diopeus, is expressed in the 

 skull as follows : — 



(a) The depression of the posterior angles of the skull (sus- 

 pensorial region) by the shortening and degeneration of the 

 quadrate ; the bones of the temporal arches remaining dis- 

 tinct but becoming very slender. This process leading to 

 extinction by the weakening of the articular region. 



(b) The gradual elevation of the facial region of the skull 

 and the lessening of the transverse diameter through the 

 vertical growth of the maxillary and the narrowing of the 



f rentals and nasals. 



tusks, the deepening of the diastema, the increasing con- 

 vexity of the alveolar edge and the development of serra- 

 tions on the edges of the teeth. 



