86 0. 0. Marsh — Cretaceous Mammalia. 



Tripriodon coelatus, gen. et sp. now 



In the present genns, the type specimen of which is figured 

 in Plate II, figures 19-21, the upper molar teeth have three 

 rows of elevations, separated by two longitudinal grooves. 

 The outer cones are tubercular, and the central and inner rows, 

 crescentic. In the type specimen, which is apparently the 

 first upper molar of the left side, there are four cones in the 

 outer row ; three, in the middle row ; and only two in the 

 inner series. The crown of the tooth is subtriangular in 

 outline, with the narrow end in front. 



The teeth of this genus resemble those of Stereognathus, 

 from the Jurassic of England. Several lower molars with two 

 rows of cones were found with the type, but the association 

 may be accidental. 



The type specimen is from the Laramie of Wyoming. It 

 represents an animal about as large as a rabbit. 



Tripriodon caperatus, sp. nov. 



A larger species, apparently of this genus, is indicated by a 

 number of teeth, some of them in good preservation, and others 

 in fragments. Among the more perfect are a number of lower 

 incisors, one of which, represented in Plate III, figures 18-20, 

 may be regarded as the type. This tooth is nearly flat on one 

 side, and strongly convex on the other. The enamel of the 

 crown is irregularly wrinkled into ridges. The flat side is more 

 nearly smooth, and was evidently placed closely against the 

 adjoining tooth, as shown in figure 19. 



Smaller teeth of the same general form and pattern were 

 also found, and these probably pertain to the species above de- 

 scribed. The two species indicate a new family, which may be 

 called the Tripriodontidw. 



The remains at present known are from the Laramie of 

 Wyoming. 



Selenacodon fragilis, gen. et sp. nov. 



The present genus is clearly allied to the one last described, 

 but may be readily distinguished from it by the molar teeth. 

 The upper molars have three rows of cones, arranged in the 

 same manner, but the elevations are smaller, more numerous, 

 and sharply pointed. All of those well developed are dis- 

 tinctly crescentic. The type specimen is an upper molar, and 

 is represented on Plate II, figures 22-24. The longitudinal 

 grooves which separate the series of cones, and the transverse 

 valleys between the crescents, are deeply cut, and this renders 



