342 O. C. Marsh—American Jurassic Mammals. 
on Plate X, figures 7 and 8. The entire premolar and molar 
series consists of only six teeth, the main features of which are ~ 
seen in the figures cited. The canine is large, nearly erect, and 
is apparently inserted by a single fang. There is a distinct 
diastema between this and the first premolar. The latter is 
small. The lower jaw is short and massive, and there is a deep 
mylohyoid groove (9). 
The’ molar teeth of Pawrodon appear to agree in the general 
features of their crowns with those of Achy yrodon and Pera- 
lestes, but the figures given by Owen of the specimens de- 
scribed under these names show them to be quite distinct from 
the present genus. 
Paurodon valens, gen. et sp. nov. 
In this genus, there were apparently two lower premolars, 
and four molars, all separated somewhat from each other. The 
premolars have a single main cusp, and a low posterior heel. 
Each is implanted by two roots. The molars have a single 
main external cone, and two low inner cusps. The mylohyoid 
groove extends from the pterygoid fossa to the symphyseal sur- 
face, which is large. The mental foramen is below the dias- 
tema between the canine and the first premolar. 
The upper jaw of this peculiar fossil is not known. 
The type specimen of this unique form is from the Upper 
Jurassic deposits of Wyoming Territory. 
The main object of the present article is to present a typical 
series of the remains of known American Jurassic mammals. 
A discussion of the closer relations of these to the mammals 
from the same formation in Europe, as well as to both older 
and more recent forms, will be reserved for the Memoir now 
in course of preparation. 
The vertebree, limb bones, and other parts of the skeleton of - 
mammals, found with the jaws and teeth here described, can- 
not yet be definitely associated with the latter, but an “attempt 
’ to do this will be made in the Memoir. 
The genera and species of American Jurassic mammals now 
known are given in the list below. All have been described 
by the writer, in this Journal. One figure, at least, of a typi- 
cal form of each new genus proposed, has also been given, 
either in the original description, or in the present article. 
The list is as follows: 
