Cope. I ^^ [August 15, 



The cuboid and navicular bones are distinct from eacb other and from 

 the cuneiforms, and the ecto- and mesocuneiform are coossified. There 

 are four metatarsals. The laterals (ii and v) are slender ; and the 

 medians are distinct but appressed, their adjacent sides being flat- 

 tened. This foot structure is remarkably advanced considering the early- 

 age, Wasatch Eocene, of the period of its existence, and the primitive, 

 tritubercular bunodont character of the superior dentition. The seleno- 

 dont types which appear first in our series of formations, the Oreodon- 

 tidiie of the White River low Miocene, present a much more primitive type 

 of foot. The camel series is remarkable for the early and continued 

 absence of the first and fifth metapodial bones. The first known of the 

 line, Poebrotherium, from the White River beds, has only minute rudi- 

 ments of them. It is probable the Pantolestes, or some member of the 

 Pantolestida3, is an ancestor of Poebrotherium, with a number of lost 

 types intervening. 



Elotheuium Aym. 



The first information respecting the structure of the feet of this genus 

 was furnished by Marsh.* He says "The radius and ulna were sepa- 

 rate or very loosely united. The third and fourth metacarpals were 

 nearly equal in size, and the second and fifth longer than the corres- 

 ponding bones of the pes. In the latter the first digit was wanting, 

 and the fifth rudimentary." This description leaves us in the dark as 

 to the development of the second digit in the posterior foot and of the 

 second and fifth in the anterior foot. The ambiguous language led me to 

 infer that there are four digits of the anterior foot of the animal described 

 by Marsh, and hence to separate it generically from Elotherium. The 

 first definite information is derived from Kowalevsky, from his great 

 memoir on the genus Anthracotherium.f He here states distinctly that 

 the genus is bidigitate, but with small rudiments of the second and fifth 

 metapodial bones. He shows also that the lunar is equally supported by 

 the magnum and unciforum. In a memoir especially devoted to this 

 genus:]: he also shows that the cuboid, navicular and cuneiforms are dis- 

 tinct, while the ecto- and mesocuneiforms are coosified, the entocuneiform 

 being absent. The structure of the tarsus in this genus is then as in 

 Pantolestes, and from this genus or one of the same family, Elotherium 

 no doubt took its origin through intermediate genera. || 



Selenodonta. 

 Oreodon Leidy. 



We owe to Leidy the following statement regarding the foot structure 

 of this genus. § What are supposed to be the bones of the forearm and leg 



* American Journal Scl. Arts, 1873, p. 487, June. 

 t Palffiontographica. 1873, p. 188, August ? 

 + Loc. cit., xxii, N. F. II, 7, p. 415. 



II I have given the structure of the anterior leg and foot In Elotherium impera- 

 tor. Bulletin U. S. Geol. Surv. Terrs., Vol. v, p. 60. 

 g Extinct Mammalia of Dakota and Nebraska, 1869, p. 72. 



