THE MA.'\1MAI.1A OF THE CINTA FOK.M ATIOX. -JOl 



surface. The iiaiiowcr internal sui-faces appear as triangular inclined planes, sepa- 

 rated by a median acute ridge extending from the point to the base of the crown. 

 The anterior of the internal surfaces forms at the base a pair of shallow pouches, de- 

 fined by a double festoon. The posterior of the same surfaces forms a single and 

 larger pouch at the base of the crown, included by a single and thicker festoon. This 

 latter in the third premolai- almost assumes the dignity of an additional lobe to the 

 crown, resembling the inteiuial lobes of the true molars." In I'rotoreodon these fes- 

 toons are not more distinctly marked on pm. 3 than on pm. 2, l)«ing only very fuiiit 

 elevations of the cingulum and single, not double, on the anterior part of the crown. 

 Pms. 3 and 4 are each implanted by three fangs, pms. 1 and 2 by two. The last pre- 

 molar has the form seen in Oreuduii and the ruminants generally ; it consists of two 

 crescents, an internal and an external and an internal, with a strong internal cingulum. 

 The outer crescent still retains the cordate shape and the trenchant edges seen in the 

 anterior premolars, and is considerably larger than the external crescents of the 

 true molars. The cingulum is not so strongly developed on the outer side, nor is the 

 external wall of the tooth so deeply concave as in Oreudon. 



The anterior premolars of Protoreodon, with their great simplicity of construc- 

 tion, are decidedly moi-e like those of Ar/riochcerus than those of Oreodon, Init the 

 fourth premolar resembles that of the latter genus, while in Ar/riochcerics it has 

 I'cached an extraordinary' degree of complication, having almost completely assumed 

 the molar pattern, and differing only in the rudiiTKJUtary state of the postero-inlernal 

 lobe. 



The molars of Protoreodon increase in size successively from the lirst to the 

 third; the crowns are very low and broad in proportion to their antero-postcrior ex- 

 tent ; the valleys are very shallow and widely' open ; the internal crescents ai'C massive 

 pyi'amids, and the horns are very faintly mai-ked ridges. The external crescents are 

 intermediate in character between those of Oreodoa and of Ar/riochoerus, in being less 

 concave and overhanging and less deeply separated by an outward extension of the 

 median valley than in the latter, more so than in the former, with an additional 

 resemblance to Oreodon in the compressed shape of the buttress between the outer 

 lobes and in the faint convex ridge which rnns up from the apex of these crescents. 

 The balance of resemblance, as far as the outer wall of the tooth is concerned, in- 

 clines therefore towards Oreodon, while the construction of the inner half of the crown 

 and the general appeai'ance of the whole is more like that of Af/riorlKma*. A very 

 imi)0rtant difference from the molars of all the oi-eoilouts liillu-rto known consists in 

 the presence of a lilili 1((1)l' situated in the anterif>r ii.ill' of ilic crown; it i-; but 

 slightly separated from the antcio-iiitciiial crescent, with wliicli it is appairnlly 



