32 



which likewise gradually expanded as a result of mastication. A continuance 



of the process would unite the inner and outer tracts, and in an advanced 

 condition of abrasion the distinction of the four lobes with the intervening 



valleys would be obliterated, leaving a broad concave dentinal surface bordered 

 by the enamel at the sides of the crown. ' 



The upper molars of Palscosyops, while presenting considerable resemblance 

 1o those of Pakeotherium, also exhibit well-marked differences. They differ 

 especially in the greater prominence and more robust character of the ex- 

 ternal buttresses of the outer lobes, in the form and more complete isolation 

 of the inner lobes, and in the absence of the deep pit at the termination of 

 the oblique valley of the crown. 



In comparison with the upper molars of Anoplotherium, those of Palaeo- 

 syops especially differ in having proportionately stouter buttresses to the 

 crown externally; in possessing but a rudiment of the antero-internal lobe as 

 existing in the former, and in the different shape and relationship of position 

 of the postero-internal lobe, which in Anoplotherium has the form nearly of 

 the contiguous outer lobe and embraces it as in the deer. 



In comparison with the corresponding teeth of Chalicotherium, several im- 

 portant differences are observable. Of the outer buttresses of the crown in 

 this genus, the posterior is the larger, but in Palaeosyops the anterior is the 

 larger. The antero-internal lobe is proportionately less prominent, and the 

 postero-internal lobe has a different shape, being nearly like that in front of 

 it, and it is completely isolated. In Chalicotherium it is more like that in 

 Anoplotherium, and it joins the fore part of the postero-external lobe. In 

 the last molar of Pateosyops the postero-internal lobe is obsolete, but in 

 Chalicotherium is proportionately as well developed as in the other molars. 



As previously intimated, it is to the upper molars of Titanotherium that 

 those of Palasosyops have most resemblance. The abrupt and deep pit near 

 the centre of the crown is absent. The rudimental lobe at the fore part of 

 the crown between the anterior principal lobes is proportionately less de- 

 veloped, and yet is more isolated from the basal ridge. In the last molar the 

 postero-internal lobe is nearly suppressed, while in Titanotherium it is still a 

 conspicuous element of the crown, though less well developed than in the 

 other molars. 



The premolars of Palseosyops undergo a successive reduction forward and 

 assume a more and more elemental condition. 



