366 PATAGONIAN EXPEDITIONS: PALAEONTOLOGY. 



species. Notoryctes has greatly reduced incisors, which in their quadrate 

 form bear a certain resemblance to those of Necrolestes. 



The canine is much the largest and most prominent tooth of the upper 

 jaw ; at the base the crown is broad and thick, but it tapers rapidly to an 

 acute point ; in shape, it is obscurely trihedral, with flattened anterior and 

 grooved inner faces, and sharp posterior edge ; the whole tooth is some- 

 what recurved. The great size of the canine is in marked contrast to both 

 Chrysochloris and Notoryctes, in which this tooth is much reduced and 

 smaller than any of the incisors. 



The premolars are three in number, and only the anterior one, probably 

 p-, differs appreciably from the molars in structure ; it is inserted by two 

 fangs and has an acutely pointed, compressed-conical crown, with tren- 

 chant anterior and posterior edges and small anterior basal cusp. The 

 succeeding five teeth are alike except in size, with trigonodont crowns, 

 which closely resemble those of Chrysochloris, but are less completely 

 hypsodont and lack the pointed, cusp-like pillar which, in the recent genus, 

 arises from the inner apex of the triangle. As in the latter, p A is the 

 largest of the grinding teeth, the molars diminishing in size posteriorly ; 

 m a is very small, though not so minute as in Chrysochloris. In Notoryctes 

 the premolars are very small and simple. 



In the lower jaw the four single-rooted incisors have laterally com- 

 pressed quadrate crowns and decrease in size from i T to i T . In Chryso- 

 chloris i T is very small and % the largest of the series, and the crowns of 

 all three are more curved and pointed, less compressed than in the fossil, 

 while in Notoryctes these teeth are almost rudimentary. The canine is 

 very large and has a high, broad, trenchant, recurved and acutely pointed 

 crown, which, when the mouth is closed, is received into a deep notch in 

 the side of the upper jaw. Ameghino states that this tooth is implanted 

 by two roots, which in the individual figured by him ('94", 107, fig. 43) 

 are very greatly swollen ; in none of the specimens of the Princeton col- 

 lection are the fangs so much swollen, though one of them is not very 

 different in this respect. In Chrysochloris the lower canine is smaller 

 than i^ and in Notoryctes it is greatly reduced. 



The foremost premolar (p^) resembles p- in form, but has both anterior 

 and posterior basal cusps. The next five teeth (p^ m ) differ from one 

 another only in size ; they are trigonodont and hypsodont, much like those 

 of the African genus, but not so high and somewhat longer antero-pos- 



