364 PROCEEDINGS OE THE GEOLOGICAL SOCIETY. [June 4, 



Mammalia. They agree in the collateral position and upward direc- 

 tion of their strong incisors ; in the depth and shortness of the hori- 

 zontal ramus ; in the backward continuation of the ascending ramus 

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

 minal position of the condyle, — the two latter characters 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 Plagiaulacc 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 Plagiaulacc 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 habit 

 common to the two and essential to their existence, it does not im- 

 press me with the idea of affinity. Por the reasons which have led 

 me to regard the nearest relationship of the fossil genus as being in 

 the direction of Hypsipry7nnus, I refer to my former communication 

 passim, and to the preceding pages. Both genera appear to be Mar- 

 supial : 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 *. The species 

 of Hypsiprymnus are strictly vegetable-feeders. 



I shall adduce a celebrated case to show how little we should be 

 authorized to pronounce with confidence on the nearest affinities of 

 Plagiaulax from the small measure of evidence we now possess. The 

 Aye- Aye {Cheiromys Madagascariensis) was discovered by Sonnerat 

 before 1782. The elder Geofi'roy and Cuvier placed it among the 

 Eodents. In 1816, BlainviUe submitted the skull and teeth, together 

 with the bones of the fore-arm, to a rigorous examination, and 

 convincingly pronounced the Aye-Aye to be a Lemurine Quadrumane. 



* " II a vecu pres de deux mois, n'ayant pour toute nourritiire que du riz cuit ; 

 il se servait, pour le manger, de ses deux doigts comme Jes Chinois, de baguettes." 

 (Sonnerat, quoted in Buffon, Supplement, torn. yii. p. 268.) The early account 

 of the French traveller has been confirmed by the later and excellent observations 

 of Dr. Sand with, who fed his captive Aye- Aye upon bananas and dates, the latter 

 of which he took to with great rehsh, gnawing the larva? of insects out of the 

 branches of trees, and feeding on them when he had the opportunity. (Sandwith, 

 Zoological Proceedings, 1859, p. 113.) 



