considered as a zoological Character. 519 



between the two natural groups of the Pedimana, but clearly 

 points out the general inferiority of the whole family to the 

 Quadrumana, in the function, as well as in the structure, of the 

 organ of prehension. 



Another and still stronger affinity between the Simiadae and 

 Didelphidae arises from the prehensile power of the tail, 

 which the great majority of these animals possess ; and it is 

 not a little remarkable, that this singular faculty should be 

 almost confined to the Pedimana ; a strong proof of the natural 

 character of this family, and of the propriety of uniting its 

 component parts more intimately than has hitherto been at- 

 tempted. Indeed, there are but three other known genera 

 (containing altogether only 6 species) which agree, in this re- 

 spect, with the Pedimana ; Synetheres, Myrmecophaga, and 

 Cercoleptes ; all of which present other striking analogies, as 

 well of structure as of habits, with the Sapajousand Opossums, 

 besides inhabiting the same climate: but their influential 

 zoological characters associate them with other groups, and 

 preclude a nearer approximation to the present family. As 

 far as regards the prehensile power of the tail itself, which, as 

 I have just observed, is almost confined to the Pedimana, and 

 forms one of their most influential and important characters, 

 it seems to be a kind of compensation which nature has given 

 these animals, to balance the deficiency of power and dexterity 

 entailed upon them by the peculiar structure of their ordinary 

 organs of prehension. The Quadrumana, which have the 

 anterior thumbs completely opposable to the other fingers, 

 and therefore possess the most perfect power of prehension in 

 the hands alone, present no instance of prehensile power in 

 the tail ; whilst, on the other hand, among the Pedimana, in 

 which the prehension of the anterior hands is seriously di- 

 minished by the absence of opposable power in the thumbs, 

 this character is possessed by no fewer than 9 out of the 15 

 genera which compose the group ; the remainder, too, em- 

 bracing, comparatively speaking, only a small number of 

 species. The general prevalence of this character among the 

 Pedimana, and its almost exclusive confinement to this group, 

 certainly constitutes one of the most curious and interesting 

 facts in this department of zoology ; and the discovery of its 

 almost exclusive confinement to this family is a striking 

 example of the important deductions which we are always 

 enabled to draw from natural groups, but which no skill or 

 penetration would enable the zoologist to discover from the 

 best constructed artificial system. 



But, to pursue the affinities which subsist between the Si- 

 miadae and Didelphidae as component members of the same 



