IN ede INE ID) I BC, 
Article XXXV.—American Jurassic Mammals; by Pro- 
fessor O. C. MarsH. (With Plates VII, VIII, LX, and X.) 
In previous numbers of this Journal, the writer has 
announced the discovery of Jurassic Mammals in this country, 
and has given brief descriptions 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 rep- 
resentatives of several hundred individuals. The remains con- 
sist not of lower jaws alone, but of various portions of the 
skull, and not a few vertebree, limb bones, and other parts of 
the skeleton. 
These fossils, although fragmentary, are usually well pre- 
served, 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 re. 
mains of mammals from the Jurassic of this country 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. 
* This Journal, vol. xv, p. 459, 1878; vol. xviii, pp. 60, 215, and 396, 1879 ; 
vol. xx, p. 235, 1880; and vol. xxi, p. 511, 1881. See, also, Proceedings British 
Association, Montreal Meeting, p. 734, 1884. 
Am. Jour. Sci.—TuirpD SERIES, Vout. XXXIIJ, No. 196.—ApRIL, 1887. 
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