199 



have lost their bone-cartilage, and are hard and brittle, though not friable. 

 They are not in the least degree water-worn, and present no appearance of. 

 having been submitted to great pressure, as is so frequently the case with the 

 ossils from the Cretaceous and Eocene formations of neighboring localities. 



MAMMALIA. 



Order Runmiantia. 

 MERYCOCHCERUS. 



Merycochcerus rusticus. 



The genus above named was originally characterized from some remains, 

 discovered by Professor Hayden during Lieutenant Warren's expedition of 

 1857, in a bed of dull, fine-grained grit, on the head-waters of the Niobrara 

 River, near Fort Laramie, Nebraska. 



Merycochcerus pertains to the same family as Oreodon, a genus character- 

 ized from a profusion of remains from the Miocene Tertiary deposit of the 

 Mauvaises Terres of White River, Dakota. The general construction and 

 form of the skull appear to be nearly the same, and such, also, is the case 

 with the number, constitution, and relative position of the teeth. There arc, 

 however, certain peculiarities distinguishing the two genera. 



The molar teeth of Oreodon have, comparatively with those of most genera 

 of existing ruminants, short crowns as in the deer; and, as in this, at matu- 

 rity they are all inserted alone by fangs. In Merycochcerus the crowns of 

 the molars are proportionately longer, and in the mature condition of the ani- 

 mal, while the anterior ones were fully protruded, the posterior ones, though 

 in functional position, were only partially protruded, and continued to advance 

 as they were worn away. The difference between the two genera, Oreodon 

 and Merycochcerus, in respect to the comparative length of the molar crowns, 

 is like that existing between the molars of the deer and the ox, but not to 

 the same degree. While the condition of the teeth of Oreodon corresponds to 

 that of the deer, those of Merycochcerus rather hold an intermediate condi- 

 tion to those of the deer and the ox. 



In Oreodon, when the last of the molar series was fully protruded so as to 

 be inserted by the fangs alone, the anterior molars might still be in a condi- 

 tion to exhibit very conspicuously the anatomical characters of their triturat- 

 ing surfaces, as displayed in Plate VII of the Extinct Mammalian Fauna of 



