Frof. 0. C. Marsh — American Jurassic Mammals. 295 



specimen, on which it is based, was originally placed by the writer 

 in the genus Tinodon, and the species named Tinodon ferox. This 

 specimen is a right lower jaw, with most of the teeth in position. 

 There are three premolars, and four molars. The premolars have 

 one main cone, pointed and compressed, with a low cusp in front, 

 and a larger one behind. The last premolar is large. The penulti- 

 mate molar has four distinct cones instead of three. The canine 

 was large, and directed well forward. The coronoid process is high, 

 and inclined backward. The mylohyoid groove is nearly parallel 

 with the lower margin of the jaw, and extends forward to the 

 symphysis. The latter is strongly mai-ked. 



Paubodontid^. 



A peculiar genus, Paurodon, widely different from any form 

 hitherto found in America, or Europe, is represented at present by 

 a single specimen, a left lower jaw. This is shown on Plate IX. 

 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 [g). 



The molar teeth of Paurodon appear to agree in the general 

 features of their crowns with those of Achyrodon and Peralestes, but 

 the figures given by Owen of the specimens described under these 

 names show them to be quite distinct from the present genus. 



Paurodon valens. Marsh. 



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 surface, which is large. 

 The mental foramen is below the diastema 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 vertebra, limb bones, and other parts of the skeleton of 

 mammals, found with the jaws and teeth here described, cannot 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 



