THE 



GEOLOGICAL MAGAZINE, 



NEW SERIES. DECADE III. VOL. IV. 



No. VI.— JUNE, 1887. 



o^aica-TiET-A-Xj -A_I^TIC!Xi:ES. 



I. — Amekioan Jurassic Mammals. 



By Professor 0. C. Marsh, M.A., LL.D., F.G.S. 



(PLATES VI. AND VII.) 



IN previous publications the writer has announced the discovery 

 of Jurassic Mammals in America, and has given brief descrip- 

 tions of the more important forms brought to light.^ Since the last 

 article on this subject, a large amount of new material has been 

 secured, including representatives of several hundred individuals. 

 The remains consist not of lower jaws alone, but of various portions 

 of the skull, and not a few vertebrge, limb bones, and other parts of 

 the skeleton. 



These fossils, although fragmentary, are usually well preserved, 

 but owing to the peculiar conditions under which they were 

 entombed, no two bones of the skeleton are as a rule found together. 

 This fact, taken in connection with the very diminutive size of the 

 animals themselves, and especially with the present brittle nature 

 of the teeth and jaws, has rendered their investigation a work of 

 great difficulty. The importance of the subject, however, and the 

 fact that all the known remains of mammals from the Jurassic of 

 America are in the collection made by the writer, have led to a 

 careful study of the whole material, and the results will be brought 

 together in a Memoir now in preparation for the United States 

 Geological Survey. 



Some of the results of this investigation, and notices of several 

 new forms recently discovered, are given below in the present 

 article. 



In connection with this work, the writer has also examined the 

 more important specimens from the Jurassic of Europe, and, like- 

 wise, the few specimens known from the Trias, in both Europe and 

 America. 



The American Jurassic Mammals hitherto found are all from 

 essentially the same geological horizon, in the Atlantosaurus beds, of 

 the Upper Jurassic. The principal locality is in Wyoming, on the 

 western slope of the Rocky Mountains, and remains of two or three 

 hundred individuals have been obtained at this place alone. At 

 other points in the same region, a few remains have been found. A 



^ American Journal of Science, vol. xv. p. 459, 1878; vol. xviii. pp. 60, 215, and 

 396, 1879 ; vol. xx. p. 235, 1880 ; vol. xxi. p. 511, 1881 ; and vol. xxxiii. p. 327, 

 1887. See, also. Proceedings British. Association, Montreal Meeting, p. 734, 1884. 



DECADE III. — VOL. IT. — NO. YI. 16 



