326 A MEMOIR ON THE EXTINCT 



ridges, separated by deep angular transverse valleys, causing the teeth to assume a re- 

 markably taperoid appearance, and indicating a movement in the lower jaw of Platygonus, 

 less rotary and more simply ginglymoid than exists in Dicotyles; for at the same 

 stage of trituration of the teeth in the latter, the principal lobes would be worn down to 

 a level with the bottom of the interlobular fissures, approaching more in this respect the 

 Hog than the Tapir. In the last molar, the fifth or posterior lobe, broken in the specimen, 

 is simple, and demiconoidal or flattened before and convex behind. Between it and the 

 internal of the second pair of lobes, is a slight tubercle, a constituent portion of the basal 

 ridge. 



In neither teeth of the specimen do constituent portions of the basal ridge exist inter- 

 nally between the lobes, but externally, portions unite the bases of the latter. 



The upper true molars (PI. 37, fig. 13,) present the same striking peculiarities which 

 distinguish them from Dicotyles, as the lower ones; that is to say, the principal lobes 

 are very robust and prominent, the accessory lobes have disappeared, and the former and 

 the basal ridge are unwrinkled. 



These teeth are quadrate, constricted at the middle laterally, have convex sides, and 

 are surrounded by a basal ridge open at the bases internally of the inner lobes. The 

 latter are trilobate as in Hippopotamus, or expand before and behind, where they come 

 in contact with the outer lobes, which are simply conoidal. In the specimens, the expan- 

 sions just mentioned are worn away, leaving the transverse pairs of principal lobes associ- 

 ated as prominent pyramidal ridges, separated by deep and wide transverse valleys, as in 

 the case of the corresponding teeth of the lower jaw. 



The basal ridge is best developed anteriorly and posteriorly, and though worn smooth 

 to some degree, yet appears never to have been so wrinkled or tuberculatcd and foveated 

 as in the Peccary. In the last molar posteriorly, it is prominently convex, and at the 

 middle rises in a simple short accessory tubercle associated with the postero-internal lobe. 



The second and third premolars (PI. 37, fig. 12,) are like one half of the true molars. 

 They are quadrate, with rounded sides and angles, and narrowest and most convex inter- 

 nally, and have a single transverse pair of lobes like those of the true molars, surrounded 

 by a cingulum open for a short space internally and externally at the bases of the cor- 

 responding lobes. The cingulum or basal ridge is nearly twice as thick posteriorly as 

 anteriorly. 



The crown of the first premolar (PI. 37, fig. 12,) is trilateral, with rounded angles, and the 

 apex forwards, and consists of a single conical lobe, surrounded at its inner four-fifths by 

 a strong basal ridge best developed posteriorly. 



Found in the same crevice with the specimens just described, was a fragment of the 

 face of a young animal containing upon the left side the three permanent premolars, which 

 had not yet protruded, the fangs of the canines, and a single lateral incisor. (PI. 38, 

 fig. 2.) This specimen Dr. Le Conte referred to Platygonus comprcssus in his memoir 

 on the latter, but subsequently, from comparison with the cave head alluded to, was led 

 to suspect it belonged to Dicotyles depressifrons.* From more prolonged cqmpa- 



l'i Vcad Nat Sci - i - 



