84 



Marsupialia — Tritylodon. 



upper teetli are usually arranged in three rows, in the lower in 

 two. Many of the earliest known mammals belong to this 

 group, but it is doubtful whether some forms from the Trias 

 that have been referred to it may not really be reptiles. For 



Fig. 106 — An upper true molar of Tritylodon Fraasii (Lydekker), from the Upper Trias of 

 Strasburg. The two central figures are of the natural size ; the others are enlarged 

 three times, o, crown surface : a, basal surface ; v, h, the two lateral surfaces 

 i, a, anterior and posterior surfaces. 



^ 



<s; 



f a 



Fig. 107. — Cranium of Tritylodon lonfjmviis (Owen), Trias, Basutoland, South Africa. 

 a=palatal view of skull, showing the dentition; 6 = view of the upper 

 surface of the skull, f nat. size. (See Table-case, No. 14a.) 



Tritylodon. instance Tritylodon longcevus, a skull of which was discovered 

 in Basuto-land in 1884, was referred by Owen to the 

 mammalia, but Seeley has lately shown that it is probably 



Microlestes. closely related to the Theriodont reptiles. As to Microlestes 

 antiquus from the Trias of Stuttgart in Germany, and 

 Microlestes Moorei discovered by the late Mr. C. Moore in 

 the Rhaetic beds of Frome, Somerset, they are known only 



