1897.] Trituberculy : 1001 
each row. Thus the upper molar of Perognathus is closely 
analogous to that of the Mesozoic Multituberculata, especially 
to such a type as Tritylodon. Passing also from the higher 
Multituberculata to the lower and more ancient, we find fewer 
and fewer cusps until we reach a “ paucitubercular” parent 
form in the upper Triassic Microlestes. Microlestes itself was 
not tritubercular; it had a basin-shaped crown surrounded by ` 
irregular tubercles; this basin, however, was not dissimilar to 
that in molars of the Eocene rodent Plesiarctomys which is ob- 
viously of tritubercular origin. 
This evidence has been recently reinforced in a most strik- 
ing manner by the discoveries of Professor Seeley in the Karoo 
Beds of South Africa, from which two principal conclusions 
may be derived: First, that Tritylodon, formerly placed with 
the mammalia, contains a large number of reptilian characters. 
Since the fossil is closely related on the other hand to the re- 
trigon 
Fig. 6.—Tricon AND TALON. Mechanical relations of tritubercular molars ; 
also homologous and functionally analogous parts. 
maining Multituberculata, it appears possible that we have in 
the Gomphodontia the group from which the Multituberculates 
sprang. A study of the dentition of other Theriodonts in the 
Karoo Beds shows that while Tritylodon and Trirachodon are 
typically Multituberculates, others, such as Diademodon have a 
trituberculate pattern, exactly such a pattern as we find in 
certain Lower Eocene mammals. Altogether there is certainly 
