APPENDIX. 



Aet. X. — A Horned Artiodactyle (Protoceras celer) from 

 the Miocene ; by O. C. Marsh. 



It is an interesting fact, that while all existing mammals 

 with horns in pairs are artiodactyles, and none of the recent 

 perissodactyles are thus provided, the reverse of this was true 

 among the early forms of these groups. The Dinooerata of 

 the Eocene, a specialized order of ungulates, as well as some 

 of the perissodactyles of both the Eocene and Miocene, had 

 horns in pairs, while no horned artiodactyles have hitherto 

 been known from either the Eocene or Miocene. 



A fortunate discovery made during the past season, in the 

 Miocene of South Dakota, proves, however, that before the 

 close of this period, one artiodactyle, at least, was provided 

 with a pair of horns. This animal was apparently a true 

 ruminant, and nearly as large as a sheep. Only a single skull 

 is known, and this, fortunately, is in good preservation, except 

 the extremity in front, which is broken off and lost. In 

 general form and proportions, this skull is of the ruminant 

 type. Its most striking feature is a pair of small horn-cores, 

 situated, not on the frontals, but, on the parietals, immediately 

 behind the frontal suture. These prominences were thus 

 placed directly over the cerebral hemispheres of the brain. 



The frontal bones are very rugose on their upper surface, 

 and this rugosity extends backward on the parietals, and to 

 the summit of the horn-cores, as well as between the latter, 

 and along the wide 'sagittal crest. The horn-cores are well 

 separated from each other, and point upward, outward, and 

 backward, overhanging somewhat the temporal fossae. They 

 are conical in form, with obtuse summits. 



Am. Jour. Sci. — Third Series, Vol. XLI, No. 241.— January, 1891, 

 5a 



