ITS DISPUTED AFFINITY. 449 



going pages to show that, to whatever family comparative 

 anatomy may ultimately consign the genus, it must always 

 be held to he a singularly modified form. I have directed 

 attention to the numerous points of analogy between the 

 lower jaw of Plagiaulax and that of the Aye-Aye, itself one 

 of the rarest and most aberrant of existing Mammalia. They 

 agree in the collateral position and upward direction of their 

 strong incisors ; in the depth and shortness of the horizontal 

 ramus ; in the backward continuation of the ascending ramus 

 in the same horizontal line with the body of the jaw, and in 

 the terminal position of the condyle — the two latter charac- 

 ters not being found, so far as is at present known, in any 

 other Mammalia, fossil or recent. They agree further in the 

 form and direction of the articular surface, in the reclinate 

 coronoid, and in the backward projection of the condyle 

 behind it. The two jaws are on the same plan of construction. 

 Starting from the deep narrow incisors of the Aye-Aye 

 carried back below the molars, the great depth of its jaw, and 

 the other associated characters, can be seen to be in necessary 

 correlation. In Plagiaulax they are all presented in a less 

 degree of development. The resemblance goes no further. 

 I doubt if in the fossil genus the lower incisors were opposed 

 in the upper jaw by only two chisel-shaped teeth as in the 

 Aye-Aye. In all the other dental characters they are widely 

 distinct. In Plagiaulax the force of the dental system is 

 manifested in the great development of the premolars, of 

 which there are none, at least in the adult state, in Cheiromys, 

 but a vacant bar instead. In the latter there are three molars ; 

 in the former, only two. While, therefore, admitting that the 

 common construction of the jaw involves some trait of hahit 

 common to the two and essential to their existence, it does 

 not impress me with the idea of affinity. For the reasons 

 which have led me to regard the nearest relationship of the 

 fossil genus as being in the direction of Hypsiprymmis, I refer 

 to my former communication passim, and to the preceding 

 pages. Both genera appear to be Marsupial : their incisors 

 are on the same morphological plan, and their premolars are 

 in the main identical, except in point of number. The Aye- 

 Aye is a nocturnal animal, which uses its strong incisors as 

 a nipping-apparatus, for breaking and detaching bark and 

 wood in pursuit of the larvae upon which, in part, it is said to 

 feed. One of the live specimens procured by Sonnerat, on 

 the first discovery of this form, lived in captivity two months 

 fed on boiled rice. 1 The species of Hypsiprymmis are strictly 

 vegetable-feeders. 



1 ' II a vecu pres de deux mois, viz euit ; il se servaif, pour le manger, 

 n'ayant pour toute nourriture que du de ses deux doigts comrue les Cbinois 

 VOL. II. G a 



