VERTEBRATE PALAEONTOLOGY IN 1909 665 



British Museum. Cope, who proposed the name Multituber- 

 culata for the group, eventually suggested affinities with the 

 monotremes, and of late years Plagiaulax and its relatives have 

 very generally been included in the Monotremata. The new 

 specimen indicates not only that the original reference to the 

 diprotodont marsupials was correct, but also shows that the 

 teeth from the English Purbeck described as Bolodoti belong 

 to the anterior part of the cheek-series of Plagiaulax, while 

 the American specimens on which the genus Chirox is based 

 occupy a similar position in the jaws of Ptilodus. 



In concluding his description of the new specimens of 

 Ptilodus in vol. xxxvi. (pp. 611-27) of tne Proceedings of the 

 U.S. National Museum Mr. J. W. Gidley remarks that: 



" Falconer and Owen referred Plagiaulax to the Diproto- 

 dontia, but differed in their opinions regarding its probable 

 habits and taxonomic relations. Falconer compared Plagiaulax 

 with Hypsiprymnus (Potorous) and sought to prove that the 

 former was a saltatory herbivorous marsupial, allied to the 

 rat-kangaroos. Owen just as strongly contended that it was 

 carnivorous in habits and more probably related to the extinct 

 carnivorous Thylacoleo. Owen's conclusions regarding the car- 

 nivorous habits of Plagiaulax lose much of their force since 

 it is now apparent that his principal arguments were based 

 on an error in the interpretation of a most important factor, 

 namely, the normal position of the jaw. Viewing the lower 

 jaw of Ptilodus properly articulated with the upper one (a and b), 

 it is observed that passing forward it pitches downward at a 

 considerable angle, bringing the plane of the tooth-row below 

 the condyle and the incisors into a semi-procumbent position 

 as in the diprodonts. It will be noted also that the greater 

 part of the thin cutting blade of p t does not come in contact 

 with the upper teeth but stands free in the mouth. If the lower 

 jaw of Plagiaulax is thus placed, the condyle is above the tooth- 

 row and not below 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 recognising the fact that the blade-like 

 premolars did not oppose teeth of like structure in the upper 



