72 PROCEEDINGS OF THE BALTIMORE MEETING 



1905 and was followed by his important discussion of this subject entitled 

 "The phylogeny and classification of reptiles/^ Journal of Geology, Au- 

 gust, 1917. In this article, which expresses his mature opinions, he de- 

 parted from his previous conservative attitude toward classification and 

 proposed to add two subclasses of reptiles, the Anapsida and Parapsida, 

 to the subclasses previously proposed by Osborn, namely, the Synapsida 

 and the Diapsida, making a fourfold grand division of the Reptilia. 

 Doubtless it was Williston's intention to fortify this system of classifica- 

 tion in his forthcoming general work on the Reptilia. 



WORK ON PRIMITIVE AMPHIBIANS AND REPTILES ^ 



In 1902, at the age of fifty, Williston was called to the University of 

 Chicago as head of the new department of vertebrate paleontology — a 

 chair which he occupied with great distinction and with continued influ- 

 ence for the remaining sixteen years of his life. He now began to con- 

 centrate his attention more exclusively on vertebrate paleontology. Dur- 

 ing the first six years he continued his studies and publications on the 

 Cretaceous reptiles; then he began to turn toward the study of far more 

 difficult and obscure problems, namely, the relatively primitive amphib- 

 ians and reptilian life of the Permian, where in several groups he marked 

 the beginnings of the higher forms which he had previously studied, as 

 well as the adaptive radiation of the lower forms to a great variety of 

 habits and habitats. 



Prof. E. C. Case, now of the University of Michigan, who was one of 

 Williston's students at the University of Kansas, had cooperated with the 

 late Prof. Georg Baur at the University of Chicago in the study of Dime- 

 trodon and other Permian reptiles and had collected for that university a 

 number of important types of pelycosaurs and cotylosaurs. After Baur^s 

 untimely death. Case continued to collect and study the Permian reptiles 

 and amphibians of Texas and other States, finally issuing his well known 

 Carnegie Institution monographic revisions of the Pelycosauria and 

 Cotylosauria, in which he revised and extended Copers work on these 

 animals and figured the types and other important specimens in the 

 American Museum of Natural History, in the University of Chicago, and 

 elsewhere. Thus Cope, Baur, Case, and Broili had opened and partly 

 explored an important field of work which Williston had long desired to 

 enter. 



Accordingly, in 1907 and 1908, Williston began to publish on this sub- 

 ject, which occupied most of the closing decade of his life and constituted 

 perhaps his greatest contribution to science. It is pleasant to record that 



° See footnote, p. 70. 



