272 PROUJiEDINGS OF THE ACADEMY OF [1883. 



arates ' regions ' from ' subregions ' should be drawn between 35 

 and 46 per cent, rather than between 46 and 63 or 64 per cent., 

 or even between 64 and 78 per cent. Prof. Heilprin has not told 

 us why, and I am unable to appreciate the reason therefor. 

 Surely it is not sufficient to answer by simply asking the question 

 put in Nature (p. 606). 



"But an analysis of more (but onl^' approximately) correct 

 figures and a more logical classification of mammals than that 

 adopted by Prof. Heilprin reveal factors materiall}^ contravening 

 the tabular statements of that gentleman. 



" First we must exclude the marine mammals, because their 

 distribution and limitation are determined by other factors than 

 those which regulate the terrestrial ones. A consideration then 

 of the terrestrial forms leads to the following results : — 



" The Arctamerican or Nearctic region has twenty-seven 

 families, of which eleven are not shared with Eurasia and four 

 are peculiar; it has sixt}' -eight genera, of which forty-five do 

 not enter into Eurasia. 



" The Eurasiatic or Palsearctic region has thirty-two' families, 

 of which seventeen are excluded from North America, and it 

 possesses eighty -nine ' genera, of which sixty have failed to become 

 developed in America. 



" Such contrasts will more than compare generally with those 

 existing between Eurasia and India, and even between the ' Tri- 

 arctic ' or ' Holarctic ' and Indian ' regions,' and the same de- 

 structive process by which the northern regions are abrogated 

 would entail the absorption of the Indian as well into a hetero- 

 geneous whole. The three can in fact be well united (as Csenogrea), 

 and contrasted with a group (Eogtea) consisting of the African, 

 South American, and Australian regions, as I long ago urged 

 {Ann. and Mag. Nat. Hist. [4], xv, 251-255, 1875), but the claims 

 of each to be considered as ' regions ' or realms are not thereby 

 affected. " Tiieo. Gill. 



*' Smithsonian Institution, Washington, May 12." 



The above criticisms of Prof. Gill fall into two distinct cate- 

 gories, which may be conveniently formulated as follows : — 



' These are the groups admitted by Prof. Heilpriu, exclusive of the 

 Pinuipeds. 



