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Pi 



TRANSACTIONS 



OF THE 



AMERICAN PHILOSOPHICAL SOCIETY 



AETICLE I. 



THE HISTOEY OF THE PELYCOSAURIA, WITH A DESCRIPTION OF THE GENUS 



DIMETRODON, COPE.*/ 



J- 

 BY <£ BAUR AND E. C. CASE. 



Read before the American Philosophical Society, March 3, 1899. 



Historical. 



The first remains of Permian Reptiles in the United States were described by Prof. 

 Cope 1 in 1875 from near Danville, Vermillion county, in eastern Illinois. It was left 

 undecided whether the strata from which the fossils came belonged to the Triassic or the 

 Permian. The vertebrate remains are unaccompanied by invertebrate fossils, but the 

 invertebrate remains of the region are all Carboniferous forms. Mr. Gurley, of Danville, 

 the discoverer of the fossils, considers that the vertebrate remains came from deposits in 

 the bed of an ancient river of the Permian time which cut through the underlying Car- 

 boniferous rocks. This, if true, explains the puzzling feature of these typically Permian 

 forms occurring on the same level with the Carboniferous invertebrates. 



The genus and species Clepsydrops colhttu Cope was established, based on cervicals, 

 including the axis, dorsal and caudal vertebras ; besides proximal ends of ribs, an 



* Prefatory Note. — The unfortunate death of Dr. Baur left the manuscript of this article in the hands of 

 the junior author in an unfinished condition, and he has attempted to complete it with as little change from the 

 original portion written by Dr. Baur as possible. The historical part, with the exception of the Russian and the 

 Bohemian forms, and a portion of the African forms, was the work of Dr. Baur. The description of the skeleton 

 was the work of the junior author, with the advice of Dr. Baur. 



A. P. S. VOL. XX. A. 



