1910.] AND THE MULTTTUBERCULATA. 7G3 



I beliftve to be r, and their tips probably rested agiiinst tlie 

 small i\ 



Between the nasals and tlie premaxillaries is a pair of well- 

 developed septomaxillaries which have not jareviously been 

 observed. The position of these bones is seen in the figures 

 given of both side and upper views. The septoniaxillary com- 

 pletely separates the jjremaxillary from tlie nasal and passes down 

 into the anterior nasal i-egion. There is no evidence that the 

 nares have been sepai-ated by a complete internasal process of 

 the premaxillaries. 



When the back part of the skull and the lower jaws are restored 

 there is presented a singidarly Rodentdike appearance. 



As regards the habits of Tritylodon, I think it most prol3;d:)le 

 that it was a root-eating animal, the large tusk-like 2nd incisoi-s 

 being well adapted for digging out and breaking ofi" the roots, 

 and the molars with their rows of crescentic tubercles admirably 

 suited for grinding. 



Tritylodon is the oldest Multituberculate mammal the skull 

 of which is known even partly, and the only other Multituber- 

 culate of which much besides the lower jaw is known is one of 

 the latest Eocene types, Ptilodus. Fortunately there has recently 

 been discovered and described by Gidley a good skull with the 

 lower jaw in position and a number of the more impoitant bones 

 of the skeleton of Ptilodus gracilis. 



From the study of Ftilodiis, Gidley comes to the following veiy 

 interesting conclusions, which maybe stated in his own words: — 

 " A fact of first importance is that neither in the skull nor 

 skeleton of the Montana specimen are there any indications of 

 affinities suggesting the Monotremes, while every character is 

 marsupial, as shown in the general arrangement and function 

 of the teeth and the development of the skull and skeleton. The 

 unequal deAelopment of the fore and hind limbs, the chai-acter 

 of the incisors, the form of the palate, and the position of the 

 cheek-teeth all indicate definite affinities with the Diprotodonts. 

 At the same time the reduction in numbers of the molars and 

 the extreme specialisation of the premolars confirms Osliorn's 

 conclusion regarding the philetic position of the group, namely, 

 that the Multitubc'rculata may be the last representatives of 

 a very ancient phylum that became extinct in the early 

 Tertiary. 



" From the foregoing therefore it appears that the Allotheria 

 repi'esent an extinct group of multituberculate Eutherian 

 mammals closely related with but not ancestral to the Diprotodont 

 division of the Marsupialia, with which division thev may now 

 be classed as an Infraorder, or Superfa.mily, their relationship 

 dating back to a common ancestry somewhere in the Jurassic or 

 even to earlier Triassic times, as was suggested by Cope."' 



While evei-yone must be most grateful for the great addition 

 made by Gidley to our knowledge of the INIultituberculate struc- 

 ture, I should like to suggest that I think the case is by no 



