4(5 MEMOIES OF THE ]SrATIONAL ACADEMY OF SCIENCES. 



south of the Great Lakes and I^ew England, his Upper Sonoran being rhe equivalent of th& 

 Carolinian of other writers, and his Lower Sonoran corresponding to the Austroriparian subprovinco 

 of Allen. Such an enormous extension of the term Sonoran seems unfortunate, and it is to be 

 hoped that it will not be generally adojjted. 



The word Mexican, being far more general in its application, is obviously a more natural 

 and general term, and means more to the general student than the restricted word "Sonoran." 

 Sonora is but a small district or portion of Mexico, and while we might perhaps retain the name 

 Sonoran for the fauna of northeastern Mexico in the sense originally intended by Professor Cope, 

 to give it the very great extension now proposed is at least inadvisable.' 



Another consideration is the probable origin of the fauna of this Arid or Plateau Province. 

 The region covered by the fauna and flora of the Great Plains of the United States (Campestrian) 

 and of the Mexican Plateau is entirely distinct from the northern or cold-humid and the southern 

 warm-humid subregions of our continent. 



It is possible that it is in a large part made up of the remnants of the Pliocene fauna, which 

 underwent great modifications during the process of desiccation of the treeless, elevated western 

 l)ortion of oar continent (originally the Mesozoic Pacifls of Clarence King). Doubtless during the- 

 period of elevation and of drainage, resnlting in the formation of the extensive desert tracts of tlie 

 United States and Mexico, when the surface became deforested, owing to the lack of sufficient rain- 

 fall, the present assemblage, or at least the immediate forerunners of the plants and animals of 

 this vast plateau region, formerly inhabitated by the lacustrian life of the Eocene, IMiocene, and 

 Pliocene Tertiary epochs — times of tropical humidity and heat — was gradually brought into 

 existence. 



The general name "Arid province" applied by Dr. Allen to this plateau region seems appro- 

 priate, and for the two quite distinct subprovinces Dr. Allen's term Campestrian is well selected, 

 and for the southern we hope the term Mexican will be reserved, especially since the tropical 

 liortious of Mexico seem, so far as our present knowledge extends, scarcely distinguishable from 

 that of Central America in general. We shall ventuie in this work to use the word Mexican in the 

 sense in which the term Sonoran has been employed by Dr. Merriani. 



The maps published by Dr. Allen in his most recent essay on the geographical distribution of 

 North American mammals (Bulletin of the American Museum of Natural History, iv, pp. 199-24:3, 

 1891!) will, with a few minor changes, serve our purpose in illustrating the distribution of the insects 

 and in a more restricted way of the Bombycine moths (see Map I). We may have in our former 

 essay contrasted too sharply the Central province and the Pacitic Coast district. 



We will first contrast our North American assemblage of Notodontida; with that of Europe, 

 including northwestern Asia (the "Paheartic" region of Sclater) and inclusive of the tropical 

 portions of southeastern Asia (Wallace's Oriental Region). We purposely omit any reference to 

 the term Nearctic, believing it an unfortunate appellation, neither philosophical nor true to the 

 fact that America is zoologically an older continent than Eurasia, its plants and animals having 

 lagged behind in development that of the flora and fauna of the Old World, geological extinction 

 having gone on more rapidly in Europe than in America, at least in northwestern America, while 

 the ending Arctic is quite inapplicable to an assemblage of north temperate animals. 



The Notodontian fauna of America is naturally richer than that of Eurasia, because of the 

 greater extent and diversity of surface of the continent over wliich it is spread. 



In Staudinger's Catalogue of European Lepidoptera of Notodontidre there are enumerated 

 1-t genera and 42 species; 'in America, north of Mexico, we have 21 genera and about 78 species. 



The'following lists will present in a graphic way the resemblances and differences between the 

 Notodontian fauna of the two hemispheres, it being understood that by Eurasia we mean Europe 

 and Asia, without the Oriental region; and by North America, that continent less Mexico and 

 Central America. 



'In his valuable essay entitled "Laws of temperature control of the geographic distribution of terrestrial 

 animals and plants," Nat. Geogr. Mag., vi, Dec, 1894, Dr. Merriam divides the United States into three regions: the 

 Boreal, Austral, and Tropicil. The Austral region is divided into three zones: the Transition, Upper Austral, and 

 Lower Austral. The Upper Austral zone comprises two principal subdivisions: an eastern or Candiuian area aud a 

 western or Upper Sonoran area. The Lower Austral zone comprises two principal subdivisions : an eastern or Aus- 

 troriparian area, and a western or Lower Sonoran area (p. 277). 



