9'^ 



1884.] ^"^ [Cope. 



The ulna and radius are coosified. The scaphoid and lunar facets of the 

 radius are well distinguished by an oblique ridge. The carpus is un- 

 known. The median metacarpals are separate ; whether the second and 

 fifth are well developed I do not know, but suspect them to be so, as in 

 Leptomeryx, since the third and fourth bear no adherent rudiments. The 

 cuboid and navicular bones are united, while the cune'iforms are distinct 

 from them and from each other, as in Leptomeryx. There are but two 

 developed metatarsals, and these are distinct from each other. Thus the 

 fore-limb in its ulno- radius exhibits a little advance over Leptomeryx ; 

 while in the separate metatarsals it is behind the latter. 



Hypisodus Cope. 



This genus is remarkable for its prismatic dentition, being the only 

 Artiodactyle presenting the character in the White River fauna.* It was 

 probably well advanced in foot characters, but of these I know but 

 little. Parts of two tarsi found with the jaws of the 2! minimus Cope, are 

 referred to the species on account of their very small size, and general cor- 

 respondence. The cuboid and navicular are coossified. Their distal face, 

 especially the navicular part, is so narrow transversely, that it is almost 

 certain that the third and fourth metatarsals are coossified, and that the 

 second and fifth are rudimental or wanting. There is no trace of facets 

 for the latter on the naviculo-cuboid. 



PofiBROTHERiuM Leidy. 



I have fully described the limbs of this genus in the Annual Report of 

 the U. S. Geological Survey of the Territories for 1873f , as seen in the P. 

 vihoni Leidy, from the White River beds, and have confirmed them from 

 a fine specimen of the P. sternhergi Cope, from the John Day or Middle 

 Miocene of Oregon. X The characters are ; ulna and radius coossified ; 

 trapezium and trapezoides present and distinct ; magnum supporting part 

 of lunar. Two distinct metacarpals, scales representing the second and 

 fifth ; navicular and cuboid bones distinct, as are the ecto- and mesocunei- 

 forms ; entocuneiform wanting. Metatarsals two, distinct ; second and 

 fifth represented by scales. 



Observations on the Phylogent. 



I have maintained || that the selenodont dentition is a derivative of the 

 bunodont, a proposition which seems unavoidable from a mechanical point 

 of view. The testimony of palaeontology is also in its f\ivor, since in 

 America the oldest artiodactyle, Pautolestes, is bunodont. Ivowalevsky in 

 the phylogenetic table give^ in his monograph of Anthracotheriumg does 



» See Cope, Annual Report U. S. Geological Survey Terrs., 1873, p. 501, where 

 the cuboid and navicular are stated to be united. 

 1 1874, p. 499. 

 J Bulletin U. S Geol. Survey Terrs. V, p. 59. 



II Journal Academy Natural Sciences, J874. See also Ryder, The Mechanical 

 Genesis of tooth forms. Proceeds. Academy Philada., 1879, p. 47. 



g 1873 (? 4), p. 152. 

 PROC. AMER. PHILOS. SOC. XXII. 117. D. PRINTED OCTOBER 22, 1884. 



