March 21, 1919] 



SCIENCE 



277 



Platecarpus and Tylosaurus. This work be- 

 came the standard for all subsequent re- 

 searches of Osbom, Wieland and others on the 

 Cretaceous fauna. It contains some ad- 

 mirable restorations of mosasaurs and other 

 fossils which may be compared with those of 

 Dollo from the Maestrichtian of Belgium. 

 The second part. Volume VI. of the Uni- 

 versity Geological Survey, covering the Car- 

 boniferous and Cretaceous, published in 1900, 

 included the Cretaceous fishes alluded to 

 above, and the Carboniferous invertebrates by 

 Joshua W. Beede. 



Williston concluded his studies of the Cre- 

 taceous fauna during the early years of his 

 professorship in Chicago, beginning in 1902. 

 Thus his work on the Kansas Cretaceous 

 fauna, following the very disjointed contribu- 

 tions of Leidy, Marsh and Cope based on in- 

 ferior material, marks the turning-point in 

 this field to the new order of description and 

 generalization based upon complete material, 

 including even the skin impressions of several 

 great mosasaurs. In his observations on the 

 mosasaurs, plesiosaurs, pterodactyles and ma- 

 rine turtles, and the birds with teeth, Odon- 

 tomithes, he placed the osteology of these 

 several animals on a much more secure basis, 

 adding a number of new generic types, such 

 as a short-necked plesiosaur, Dolichorhynchops 

 osiomi. 



His first contribution to the phylogeny and 

 classification of the Reptilia as a whole ap- 

 peared in 1905 and was followed by his im- 

 portant discussion of this subject entitled 

 " The Phylogeny and Classification of Rep- 

 tiles," Journal of Geology, August, 1917. In 

 this article, which expresses his mature opin- 

 ions, he departed from his previous conser- 

 vative attitude towards classification and pro- 

 ix>sed to add two subclasses of reptiles, the 

 Anapsida and the Parapsida, to the subclasses 

 previously proposed by Osborn, namely, the 

 Synapsida and the Diapsida, making a four- 

 fold grand division of the Reptilia. Doubt- 

 less it was Williston's intention to fortify this 

 system of classification in his forthcoming 

 general work on the Reptilia. 



WORK ox 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 paleon- 

 tology, a chair which he occupied with great 

 distinction and with continued influence for 

 the remaining sixteen years of his life. He 

 now began to concentrate 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 towards the study of 

 far more difficult and obscure problems, 

 namely, the relatively primitive amphibian 

 and reptilian life of the Permian, where in' 

 several groups he marked the beginnings o£ 

 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. 



In 1911 he published from the University 

 of Chicago Press his volume, " American Per- 

 mian Vertebrates," which comprises a series 

 of monographic studies on some of the genera 

 already noted. This work contains many new 

 and original plates. His principal publica- 

 tion in 1914 was the book on " Water Reptiles 

 of the Past and Present," in which his life- 

 work on these animals was admirably com- 

 bined ^nth the results obtained by other work- 

 ers. Williston had shown a bent for the har- 

 monious study of form and function, of struc- 

 ture and habit, of environment and adapta- 

 tion, which he applied with skill and origi- 

 nality to the interpretation of the highly di- 

 versified forms of aquatic life. He followed 

 Eberhard Fraas of Stuttgart in making a 

 special study of aquatic adaptations in the 

 vertebrates; consequently his book on the water 

 reptiles constitutes one of the most important 

 contributions which we have on this subject. 

 In 1917 he bc^an a general work on the 

 "Reptiles of the World. Recent and Fossil," 

 upon which he was actively engaged up to his 

 last illness; also the publication of his papers 

 on Edaphosaurus. on the atlas-axis complex 

 of reptiles, and, equally important, his brief 



5 See footnote, p. 276. 



