ACADEMY OF SCIENCES.] PUBLISHED RESULTS. 125 



origin from some primitive cotylosaurian; like the Chelydosauria, as Case has forcefully shown. The turtles occupy 

 a phylum distinctly their own, no more intimately related to the plesiosaurs than they are to the ichthyosaurs or 

 rhynchocephalians. I can not accept the contention of McGregor that the Iehthyosauria had a primitively sauro- 

 crotaphous (I need not apologize for the word) type of skull, but would rather believe that; they, too, enjoyed a 

 genealogical line all their own from the most primitive type of reptiles, and that they should no more be grouped 

 with the dinosaurs and crocodiles than with the plesiosaurs and theriodonts." 



A very excellent final summary of Williston's knowledge and beliefs concerning the 

 Sauropterygia, both plesiosaurs and nothosaurs, is given in his book on the water reptiles (1914). 

 It is to be regretted, however, that his more ambitious project of monographing the group in 

 full was not carried to completion, though much that he did was of morphologic value. 



DINOSAURS. 



Prof. Williston wrote but little of the dinosaurs, and that mainly upon the two genera Clao- 

 saurus and Stegopelta which have been preserved in the marine Cretaceous of Kansas. His 

 early papers are brief ones: "American Jurassic Dinosaurs" (1878), l "Are Birds derived from 

 Dinosaurs" (1879), 2 and "Note on the Pelvis of Cumnoria (Camptosaurus) " (1890) .* In 1898, 37 

 in the same volume of the Kansas Geological Survey which includes his great work on the mosa- 

 saursy he discusses dinosaurs in general, and specifically the Claosaurus agilis from the Niobrara, 

 with Marsh's restoration of Trathodon {Claosaurus) annectens by way of illustration. There is, 

 however, no new information contained in the paper. 



Another article in 1898 i5 is on the sacrum of Morosaurus, a brief morphological description 

 of a specimen in the Kansas Museum. In 1899 Williston conducted ail expedition to the 

 Freeze Out Hills of Wyoming (Morrison formation) , and it was then and there that the reviewer 

 first met him. The party collected the more familiar Morosaurus, Diplodocus, and Stegosaurus, 

 and a carnivore, Creosaurus, which is the subject of a brief paper published in 1901. 55 In it 

 Williston discusses the distinctions, which are by no means clear, between Creosaurus and 

 Allosaurus, and concludes that his specimen, of which he has the nearly complete fore limb, 

 belongs to the former genus because of the very slender scapula. He also comments on the age 

 of the so-called Atlantosaurus beds of Marsh, now held to be Morrison, and believes that they 

 should bear the name Como, unhesitatingly referring them to the lower Cretaceous. 



In 1905 76 Williston published his most notable contribution to dinosaurian discovery 

 when he described a new genus of armored dinosaurs, Stegopelta, from the Cretaceous of Wyo- 

 ming. This dinosaur, which comes from what Williston has called the Hailey shales, has been 

 further and much more minutely described by Roy L. Moodie in 1910, and proves to be one of a 

 rather extensive group of forms sharply distinct from the aberrant Stegosaurus which has 

 given its name to the armored dinosaurs as a whole. In 1910 93 Williston, with Pierce Larkin, 

 described a new sauropod dinosaur from the Trinity Cretaceous of Oklahoma, of interest as one 

 of the two last recorded instances in time of the American Sauropoda. 



That Williston had further unpublished ideas of great value on the dinosaurs was evident 

 from his verbal discussions of the group. It is to be hoped that in his incompleted work on 

 the reptiles many of these opinions are recorded. They are of course included in his several 

 reptilian classifications, notably the table of 1917 (facing p. 133). 



CROCODILIA AND CHELONIA. 



Williston made a number of contributions to our knowledge of the crocodiles and turtles, 

 mainly, however, in connection with other forms of the same faunal horizons. For instance, 

 in his 1898 work on the fauna of the Niobrara Cretaceous, one finds four pages devoted to croco- 

 diles, 38 a general statement concerning the group, and a specific description of the only Kansas 

 form, Hyposaurus vebbii Cope. The turtle section of the same work, pages 351-369, is only in 

 part the work of Williston, 40 the remainder being from the pen of Prof. Case. The former 

 discusses the turtles of the Chalk and the appearance of the group in time, by way of introduc- 

 tion. Ho then passes to a morphological description of Desmatochelys lowii. There are no gener- 

 alizations on either the Chelonia or the Crocodilia until the work on "Water Reptiles of the 

 Past and Present" (1914). 



