46 
MEMOIES OF THE NATIONAL ACADEMY OF SCIENCES. 
south of the Great Lakes and New England, his Upper Sonoran being rhe equivalent of the 
Carolinian of other writers, and his Lower Sonoran corresponding to the Austroriparian subprovince 
of Allen. Such an enormous extension of the term Sonoran seems unfortunate, and it is to be 
hoped that it will not be generally adopted. 
The word Mexican, being far more general in its application, is obvioiisly 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 
portion of our continent (originally the Mesozoic Pacifis of Clarence King). Doubtless during the 
period of elevation and 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 and animals of 
this vast plateau region, formerly inhabitated by the lacustrian life of the Eocene, IVIiocene, 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 sid)provinces Dr. Allen’s term Cami^estriau is well selected,, 
and for the southern we hope the term Mexican will be reserved, especially since the tropical 
portions of Mexico seem, so far as onr present knowledge extends, scarcely distinguishable from 
that of Central America in general. We shall venture in this work to iise the word Mexican in the 
sense in which the term Sonoran has been employed by Dr. Merriam, 
The maps j)ublished 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, pj). 199-243, 
1892) will, with a few minor changes, serve our x^ni'P^*^® i'l illustrating the distribution of the insects 
and in a more restricted way of tlie Bombycine moths (see Map I). We may 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 Notodontidm with that of Europe, 
including northwestern Asia (the “Paheartic” region of Sclater) and iuclusive of the tropical 
portions of southeastern Asia (Wallace’s Oriental Region). We purposely omit any reference to 
the term Nearctic, believing it an uufortnuate apx)ellatiou, 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 which it is vspread. 
In Staudinger’s Catalogue of European Lepidoptera of Notodontidm there are enumerated 
14 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 difierences 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. 
I 111 liis valuable essay entitled ^^Laws of temperature control of the geographic distribution of terrestrial 
animals and jjlants,” Kat. Geogr. Mag., vi, Dec,, 1894, Dr. Merriam divides the United States into three regions: the 
Boreal, Austral, and Tropical. 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). 
