THE MAMMALIA OP THE DEEP RIVER BEDS. 93 



PEOTOHIPPUS Leidy. 



Proc. Acad. Nat. Scl, Philadelphia, 1858, p. 26. 



PrtOTOinppus sej [rarer us Cope. 



Bull. U. S. Oeol. and Geogr. Surv., No. 1, 1874, p. 13. 



This specimen was found by Prof. Cope's collector in the Deep River beds, and 

 is represented in our collection by a number of teeth and limb bones, which add 

 nothing to our knowledge of the species. 



PllOTOlIlPPUS sp. 



(PI. II, Fig. 17.) 



A smaller species than P. sejunctus is indicated by several specimens, none of 

 which, unfortunately, are associated with teeth, so that we cannot tell whether they 

 should be referred to any of the species from the typical Loup Fork horizons. The 

 most characteristic specimen consists of the distal part of the ulno-radius, the proxi- 

 mal row of carpals and the heads of mcs. iii and iv. The radius may at once be dis- 

 tinguished from that of Dtsmalippus by the more equine shape of the distal portion, 

 where the shaft is more flattened and less trihedral, with relatively greater transverse 

 and less antero-posterior diameter. The ulna, the distal end of which, at least, is 

 coossified with the radius, is more reduced than in Desmatippus, and, judging from 

 the marks on the shaft of the radius, the shaft was interrupted. 



Comparing the carpus of this specimen with that of MioMppus, we may observe 

 important advances and modernizations. In the scaphoid, the width and antero- 

 posterior depth are relatively increased ; the proximal articular surface is reflected 

 upon the palmar side, where it forms a small facet, articulating with a corresponding 

 one on the radius in extreme flexion. That the trapezium was present is shown by a 

 small facet on the scaphoid. The lunar has increased in dorso-palmar diameter and 

 the posterior knob, which in MioMppus is a mere knob and does not carry any of the 

 magnum facet, is very much more prominent and the distal facet is extended upon 

 it, so that the latter has gained much in extent from before backward. The cunei- 

 form is like that of ISquus in almost every respect, except that it is more compressed 

 and less massive, the upper pisiform facet is somewhat larger and the lower somewhat 

 smaller. The pisiform is decidedly more equine than that of Miohippus, both in its 

 much greater vertical height and in the separation of the two cuneiform facets, which 

 in the latter are still connected. It has not attained, however, the full vertical 

 diameter seen in the horse. 



The median metacarpal is much expanded, and especially the palmar portion is 



