92 0. C. Jlarsh — Eastern Miohippus Beds. 



The next Tertiary horizon higher up has been regarded by 

 the writer as of Pliocene age, and named the Pliohippus beds, 

 from one of the characteristic equine genera contained in it. 

 This horizon is a very extensive one, and has been identified 

 by the writer at various points along the eastern side of the 

 Rocky mountains, from Canada to the Gulf of Mexico. 

 Essentially the same deposits were likewise found by the 

 writer in 1871 above the JVIiohippus beds in Oregon. Strata 

 of still later age, named by the writer the Equus beds, occur in 

 the same regions, east and west, often covering the Pliohippus 

 deposits. 



Among the fossils of the eastern Miohippus beds, the artio- 

 dactyle mammals play an important part, and a few of the more 

 interesting of these are noticed in the present article. The 

 Protoceras family is of paramount interest, and the specimens 

 in the Yale Museum promise to add considerable to what is now 

 known of this group. The interesting family Agriocho&ridas, 

 also occurs in this horizon. 



Another family, the Anthraeot/ieridce, is well represented, 

 and contains some of the largest mammals of the horizon. 

 Two of these, briefly noticed below, are now known only by 

 fragmentary remains, some of which are characteristic. The 

 two figures in the text show respectively a last upper molar of 

 each of these animals. A comparison of these figures indicates 

 that the two animals were quite distinct from each other, 

 although about the same size, and perhaps nearly related. 



Octacodon valens, gen. et sp. now 



The tooth represented natural size in figure 1 below may be 

 regarded as the type of the present genus and species. It is 

 the last upper molar of the right side, and is in fine preserva- 

 tion. The slight wear of the tooth shows that the animal was 

 adult. There are five main cusps in the crown, two on the 

 posterior half, and three on the anterior, the antero-median 

 cusp being the smallest. On the outer margin of the tooth 

 are three prominent buttresses with conical summits, making 

 in all eight prominences on the crown, which feature has 

 suggested the generic name. 



The three conical buttresses on the outer border of this 

 tooth, all strongly developed, will serve to distinguish it from 

 the corresponding molar ol Hyopotamus, which in several 

 respects it resembles. In that genus, the main cusps are 

 much more elevated. Heptacodon, perhaps an allied form, 

 has a similar buttress at the anterior angle, but none at the 

 posterior. An upper incisor found with the present tooth, 

 and doubtless pertaining to the same individual, has a very 

 short, compressed crown, with a strong inner basal ridge, 

 making the inner face deeply concave. 



