1862.] FALCONER PLAGIAULAX. 349 



Charles Lyell's * Manual of Geology' (1857, p. 17). On both occa- 

 sions I arrived at the conclusion that " Plagiaulaoc may be regarded 

 in the natural system as a Marsupial form of Rodent*, constituting 

 a pecuHar type of the family to which Hypsijprymnus belongs," 

 although widely distinct from that genus. 



The only comment impugning this determination that has come 

 under my notice, appeared in the Article " Palaeontology," by Pro- 

 fessor Owen, in the 8th edition of the 'Encyclopaedia Britannicaf/ 

 published in January 1859, and subsequently reproduced as a sepa- 

 rate work J. The two accounts differ in some unimportant particu- 

 lars. I here cite the later in date, as presumably conveying the 

 latest views of the author. The following are extracts : — 



"Two specimens exemplified the shape and proportions of the 

 entire jaw of this species [Plagiaulaoc BecJclesii'], The foremost 

 tooth is a very large one, shaped like a canine, but implanted by a 

 thick root in the fore part of the jaw, like the large lower incisor of 

 a Shrew or Wombat. The three anterior teeth in place have com- 

 pressed trenchant crowns, and rapidly augment in size from the first 

 to the third. They are followed by sockets of two much smaller 

 teeth, shown in other specimens to have subtuberculate crowns re- 

 sembling those of Microlestes. The large front tooth of Plagiaulaoc 

 is formed to pierce, retain, and kill ; the succeeding teeth, like the 

 carnassials of Carnivora, are, like the blades of shears, adapted to cut 

 and divide soft substances, such as flesh. As in Carnivora, also, these 

 sectorial teeth are succeeded by a few smaU tubercular ones. The jaw 

 conforms to this character of the dentition. It is short in proportion 

 to its depth, and consequently robust, sending up a broad and high 

 coronoid process, for the adequate grasp of a large temporal muscle ; 

 and the condyle is placed below the level of the grinding teeth, — a 

 character unknown in any herbivorous or mixed-feeding Mammal ; 

 it is pedunculate, as in the predaceous Marsupialia, whilst the lever of 

 the coronoid process is made the stronger by the condyle being carried 

 further back from it than in any known carnivorous or herbivorous 

 animal. The angle of the jaw makes no projection below the condyle, 

 but is slightly bent inward, according to the Marsupial type." 



" In the general shape and proportions of the large premolars and 

 succeeding molars, Plagiaulaoc most resembles Thylacoleo (fig. 173, 

 pm,l and 2), a much larger extinct predaceous Marsupial from tertiary 

 beds in Australia. But the sectorial teeth in Plagiaulax are more 

 deeply grooved ; whence its name. The single compressed premolar 

 of the Kangaroo-rat is also grooved ; but it is differently shaped, and 

 is succeeded by four square-crowned, double-ridged grinders, adapted 



* I leave the words as they originally stood ; but my meaning would have been 

 more accurately conveyed by the expression " Eodent type of Marsupial," — rodent 

 being here used in the large sense, having reference to the plan of dentition, cha- 

 ra<;terized by two collateral incisors in the lower jaw, as typically shown in the 

 placental series by the Bodentia and Cheiromys; and in the Marsupialia by 

 Phascolomys, modified in the Macropodidce and the Phalangistidce by the opposi- 

 tion, in the upper jaw, of several incisors. (See Cuvier, Oss. Foss., 4th edit, 

 torn. V. p. 8.) 



t Vol. xvii. p. 161. + Palseontology, 2nd edit. p. 353. 



