THE MAMMALIA OP THE DEEP KIVER BEDS. 109 



which he obtained at Steinheim to the species of Palceomeryx occurring at that 

 locality. 



In the type specimen of B. antilopinus all the premolars are more or less injured ; 

 p-i appears to be altogether absent ; M is represented only by the fangs, but enough 

 remains of pjs and p^ to show that they differ only in size from those of B. borealis. 

 Compared with the corresponding teeth of such European species as Palceomeryx mag- 

 nus and P. sansaniensis, these premolars are distinguished by the better development 

 of the deuterocone, the narrower valleys and the character of the cingulum, which is but 

 faintly marked on M and absent from pj?. The latter tooth is the largest of the 

 series, exceeding M not only in antero-posterior but also in transverse diameter. 

 The molars increase progressively in size from the first to the third, and in all the 

 transverse width is but slightly less than the antero-posterior length, and the cingu- 

 lum is confined to the front face of the antero-internal crescent. The anterior and me- 

 dian external pillars (para- and mesostyles) are prominent. The median rib on the outer 

 face of the antero-external crescent is also conspicuous, though on m. t this ridge is less 

 prominent than in B. borealis ; the rib of the postero-external crescent is almost 

 obsolete. The internal pillar increases in size from m. \ to m. 3 , being much larger on 

 m. 3 than on either of the other molars ; in B. borealis this pillar is very small or 

 absent on m. 3 and larger on m. l and m. a . The internal crescents of the molars are 

 much like those of B. borealis; the anterior one is less complete than the posterior, 

 its hinder horn being especially shortened; on m. 3 the adjacent horns of the two 

 internal crescents are curiously crenulate, in a way that recalls the transverse crests 

 on the upper molars of some of the extinct horses. In B. borealis this does not 

 appear to be the case. The upper molars of the Sansan species differ from those of 

 the Montana forms principally in the much better developed cingulum, which em- 

 braces the entire crown of the tooth except on its outer side, and in the less devel- ' 

 oped internal pillar, which is hardly more than indicated in Fil hoi's figures. The 

 inner crescents are not crenulate and are less complicated by spurs which invade the 

 valleys, and the valleys themselves are more widely open. The P. furcatus from 

 Steinheim which Fraas has figured (ISTo. 1G, PI. VIII, Fig. 9) is more like the 

 American species in regard to the structure of the upper molars, so far as can be 

 judged from the drawings. This species is also of interest as showing a mode of 

 formation of the internal crescent of M, which I have elsewhere shown to be charac- 

 teristic of Procamelus. (No. 34, p. 436), viz, by the coalescence of two distinct ridges 

 in the median transverse line, instead of what is much more usual in the Artiodactyla 

 and universal in the case of M, by the extension of ridges from the internal cusp or 

 deuterocone. 



