NO. 16S9. THE FOSSIL CiENUS rTTLODrS—GIDLEY. 625 



(see fig. 9), here also the condyle is above the tooth-row and not be- 

 low it, as stated by both Owen and Falconer. The premolar teeth 

 likewise drop away from the level of the molar series, forward, so 

 that the anterior ones could scarcely have come in contact with any 

 teeth of the upper jaw. It is further observed that, as in Ptilodus^ 

 the ridges on the sides of the cutting blades viewed laterally run 

 nearly at right angles to the plane of the molars; thus these ridges 

 which have always been described as being " oblique " in the fossil 

 forms, are after all placed in the same relative position in the mouth 

 as those of the ridged premolars of living species. Assuming this 

 position for the lower jaw and recognizing the fact that the blade- 

 like premolars did not oppose teeth of like structure in the upper 

 jaw, the carnivorous characters pointed out by Oavcu seem to disap- 

 pear, while the general resemblances to the less 

 specialized Diprotodonts become more than 

 ever apparent. 



The resemblances pointed out by Falconer " 

 between Plaijiaulax and Potorous (" Ilypsi- 

 i)rvmnus ") a genus of the Macropodidte, are ,, 

 in the main substantiated in the present speci- of i'laoiallax bkcklio- 

 men of Ptilodiis. which also possesses some •'*'^ falconior. inner 



' . ^ . VIEW. About NAT. SIZE. 



nnportant characters in common with some of 



the Phalangerida?, as Trichosurus and Phalangcr. The specializa- 

 tion of the teeth, however, has been carried to a greater degree, both 

 in reduction in numbers of the molars and in the development of the 

 premolars, than in any of the living Diprotodonts. 



This preliminary study leads apparently to the following conclu- 

 sions regarding the zoological position not only of Pfl/odii.s and the 

 Plagiaulacidse, but of the Allotheria in general. A fact of first im- 

 portance is that neither in the skull nor skeleton of the Montana 

 specimen are there any indications of affinities suggesting the Mono- 

 tremes, while ever}^ character is marsupial, as shown in the general 

 arrangement and function of the teeth and the development of the 

 skull and skeleton. The unequal development of the fore and hind 

 limbs, the character 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 specialization of the premolars confirms 

 Osborn's conclusion regarding the philetic position of the group, 

 namely, that the Multituberculata may be the last repi'esentatives 

 of a very ancient phylum that became extinct in the early Tertiary. 



From the foregoing therefore it appears that the Allotheria repre- 

 sent an extinct group of multituberculate eutherian mammals closely 



" Quart. Journ. Geol. Soci. London, XIII, 1857. 



