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further back than the general line of the other fingers, and has, on 

 that account, when superficially noticed, the semblance of being 

 opposed to them ; but, as has been correctly observed by D'Azara 

 with reference to Ceb. capucinus, it is less separated than in Man : 

 it is, besides, of precisely the same slender form with the rest, is 

 weaker than them, absolutely without power of opposition to them, 

 and habitually acts in the same direction with them. The impres- 

 sion derived from contemplating the hands of the Old World Mon- 

 keys might induce the belief that the extremities of the Cebi are si- 

 milarly constituted : but if the knowledge that in Mycetes, Pithecia, 

 &c., there are no opposable thumbs, lead to a close observation of. 

 the anterior extremities of the Cebi, it will be found that they do 

 not act as hands, and cannot be considered as possessing the powers 

 of those organs. From innumerable observations of many species 

 of that genus Mr. Ogilby states that it was very evident, notwith- 

 standing the fallacious appearance occasioned by the backward posi- 

 tion of the organ, that they had not the power of opposing the 

 thumb to the other fingers in the act of prehension : and, in fact, 

 their principal power of prehension seems to be altogether indepen- 

 dent of the thumb, for, generally speaking, that member was not 

 brought into action at all, at least not simultaneously with the other 

 fingers, but hung loosely on one side, as Mr. Ogilby has seen it do, 

 in like circumstances, in the Opossums, Phalangers, and other ar- 

 boreal Mammals : when actually brought into play, however, the 

 thumb of the Cebi invariably acted in the same direction as the other 

 fingers. Cebus consequently agrees in the character of non-oppos- 

 ableness of thumb with the nearly allied genera. And in this hi- 

 therto unsuspected peculiarity zoologists obtain a far more impor- 

 tant character by which to distinguish the Monkeys of the Old and 

 New World than that hitherto relied on, the comparative tliickness 

 of the septum narium, or than the accessory aids afforded by the 

 absence of cheek-pouches and callosities. Hence, according to 

 Mr. Ogilby, as the Monkeys of America have now been ascertained to 

 be destitute of anterior hands, they can be no longer included among 

 the Quadrumana; and he proposes in consequence to regard them as 

 Pedimana. H& considers that in the latter series, the Monkeys of 

 America form a group parallel to that of the Monkeys of the Old 

 World among the Quadrumana : and viewing the Quadrumana as 

 consisting of two primary groups, that of which Simia forms the 

 type, and the Lemuridce, he proceeds to analyse the Pedimana in 

 order to determine whether any group analogous to the Lemurs 

 exists in it. He finds such a group in the association of the genera 

 Didelphis, Cheironectes, Phalangista, Petaurus, and Phascolarctos, 

 (together with a new genus, Pseudochirus, which he has found it 

 necessary to separate from Phalangista as at present constituted) ; 

 and for this association he uses the name of Didelpliida. Aware 

 that the modifications observable in the dentary systems of these 

 several genera have been regarded by many zoologists as betoken- 

 ing a difference of regimen, which has led to their being viewed as 

 constituting distinct families ; he, in the first place, states, as the 



