46 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



south of the Great Lakes and New Englauil, liis Upper Souorau being the equivaleut of the 

 Carolinian of other writers, and his Lower Souorau correspondiug to the Austroriparian snl)i)rovinL'e 

 of Allen. Such au enormous extension of the term Souorau seems unfortunate, aud it is to bo 

 hoped that it will not be generally adopted. 



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 "Souoran." 

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

 Souorau for the fauna of northeastern Mexico in the sense origiually intended by Professor Cope, 

 to give it the very gre-at 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 (Canipestrian) 

 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 

 portion of our continent (origiually the Mesozoic Pacifis of Clarence King). Doubtless during the 

 period of elevation aud of drainage, resulting in the formation of the extensive desert tracts of the 

 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 aud animals of 

 this vast plateau region, formerly inhabitated by the lacustriau life of the Eocene, Miocene, aud 

 Pliocene Tertiary epochs — times of tropical humidity aud 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 Canipestrian is well selected, 

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

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

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

 sense in which the term Souorau has been employed by Dr. Merriam. 



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

 North American mamuuils (Bulletin of the American Museum of Natural History, iv, pj). 109-243, 

 1892) 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 uuiy have in our former 

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



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

 including northwestern Asia (the "PaliBartic" 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 tlie 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 I'^urasia, because of the 

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



In Staudinger's Catalogue of European Lepidoptera of Notodontida- there are enumerated 

 1-4 genera and 42 species; in Ameripa, north of Mexico, we luive 21 genera and about 78 sjjecies. 



The following lists will present in a grajjhic way the resend)lances and diflerences between the^ 

 Notodontian fauna of the two hemis))heres, it being understood that by Eurasia we mean Europe 

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

 Central America. 



' lu his valuable essay entitled "Laws of temperature coutrol of the geographic distribution of terrestrial 

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

 lioreal. Austral, and Tropical. The Austral region is divided into three zones: the Transition, Upper Austral, and 

 Lower Austral. The Upper Austral zone eoni)irises two prineijial subdivisions: an eastern or Candinian area and a 

 western or Upper .Souoran area. The Lower Austral zone coin[)rise3 two principal subdivisions: au eastern or Aus- 

 troriparian area, and a western or Lower .Sonoran area (p. 1'77). 



