THE DIURNAL LEPIDOPTEEA. 437 



Dr. Sclater estimates the birds of the Australian region at 

 1000, or one species to every 3000 square miles ; the number of 

 butterflies is 725, or one to every 4138 miles. 



V. Nearctic or North- American Region. 



"J?a:^e7j^.— Greenland and North America down to centre of 

 Mexico; area of perhaps 0,500,000 square miles." 



Oharacteristic forms. — (Ends (circumpolar), Oraj)ta, Midea. 



The poverty of this region, as compared with every other, is 

 most remarkable. Many of the characteristic forms of the Pal«- 

 arctic fauna are absent in North America, although the Palsarctic 

 region has representatives of every North-American genus except 

 a few representatives of the characteristic forms of Southern 

 America. The few genera mentioned above are the only ones in 

 which the number of species is slightly greater than in the Palje- 

 arctic region. 



While the number of birds in the Nearctic region is estimated 

 at 600, or one in 9000 square miles, that of the butterflies is only 

 480, or not more tlian one in about 13,800 miles. It thus appears 

 that though North America has so few characteristic forms, yet 

 it is richer than the Palaearctic region in the number of its species 

 as compared with its extent. It must be remembered, however, 

 that this is owing partly to the sameness of the Palsearctic region,' 

 and partly to the European fauna being better known than the 

 American, and to the slighter characters on which species are esta- 

 blished by American Lepidopterists : 300 good species occur in 

 Europe alone ; and it may well be doubted whether America, east 

 of the Eocky Mountains, produces more. California and Chili, 

 though the former is necessarily included in the Nearctic and the 

 latter in the Neotropical region, do not really belong to them, 

 but are rather to be regarded as outlying portions of the Palae- 

 arctic region, many Palaearctic forms being represented in the 

 New World in these districts only. 



VI. Neotropical or South- American Megion. 

 ^ "^a;^ew/;.— West-India islands, Souther^ Mexico, Central Ame- 

 rica and whole of South America, Galapagos Islands, Falkland 

 Islands ; estimated area of about 5,500,000 square miles." 



I have found it expedient to credit tlie Neotropical region with 

 the whole of the Mexican Rhopalocera ; for all the described spe- 

 cies, with very few exceptions, if we omit the species common to 



