174 MICHIGAN SURVEY, 1908. 



I. Genera Common to the Eastern and Western Continents. 



II. Genera Peculiar to America. 



III. Species Common to the Atlantic and Pacific Slopes of the Continent. 



IV. Species Found in Russian America and in the Eastern Continent, not 

 Introduced and not Found in Atlantic America. 



1862. p. 336. "Some of the more conspicuous and peculiar species are des- 

 cribed below: enough has been stated to show that the affinities of the fauna 

 [of Lower California] are with that of the region extending from the Colorado 

 Desert across to the Rio Grande valley, thereby confirming the results obtained 

 by Prof. Baird, and Mr. Cope from the study of the vertebrata collected by Mr. 

 Xantus. 



"The limited number of species of these two classes precludes the possibility 

 of the occurrence of many new forms in the region here treated of; but in the 

 number of peculiar species of the much more extensive class of insects seen 

 in Mr. Xantus' collections, we recognize that lower California constitutes one 

 or more provinces of the Interior district, as defined by me in the introduction 

 to my synopsis of the Coleoptera of Kansas and New Mexico. 



"The preponderance of Tenebrionidae, both in genera and species seen in the 

 fauna of Upper California and Arizona, has here been partially destroyed. The 

 genera which survive are, however, such as are already known from the last 

 mentioned region. None of those peculiar to maritime California have as yet 

 occurred." p. 336. 



1878: pp. 447-448. "The elevated interior region of North America presents 

 peculiarly favorable opportunities for the study of some of the most interesting 

 questions connected with geographical distribution of animals and plants. 



"If the materials at our hands be, as indeed they yet. are. a very scanty 

 representation of the organic forms now living in that part of the continent, 

 they are, at least, sufficient to indicate the direction in which investigations 

 should be pushed, in order to arrive at definite and final results. 



"The peculiarly favorable circumstances to which I chiefly refer at present 

 are dependent on the following points in the development of the region: — 



1st. The gradual enlargement of the land-surface at the expense of the 

 pircumambient seas during the latest Mesozoic periods. 



2d. The gradual elevation of the middle of the continental mass during post- 

 Cretaceous times, so as to greatly modify the climate in respect to both moisture 

 and temperature. These changes have been so gradual, that we may say with 

 certainty (excluding the local eruptive phenomena, which were more numerous, 

 but not remarkably different from those of the present age) there has been 

 no great or paroxysmal disturbance destructive of the land-surface in the 

 elevated plains east of the Rocky Mountains since the deposition of our early 

 Cretaceous strata (Dakota Group). 



3rd. While, during the Glacial epoch, the valleys of the mountains were 

 filled with glaciers of moderate size, and the line of permanent ice streams 

 and fields brought to a much lower level, there was an absence of the extensive 

 ice sheets and flooded areas, which in Eastern America destroyed entirely the 

 terrestrial organized beings of the former period. 



"It must be inferred from the first and second of these premises that the 

 new land exposed by this gradual development of the continent received its 

 colonies of animals and plants from the conterminous older land-surfaces in 

 various directions, and that the subsequent elevation of the continental mass, 

 by which the moisture was diminished, caused a later invasion of the territory 

 by those genera and species which are characteristic of arid regions. 



"We may also conclude, from the third premise that the .glacial displacement 

 of species in the Rocky Mountains has been much less than in Eastern America, 

 and that a very small area would be left bare of life on the return to a normal 

 temperature; consequently, the previous occupants of the higher mountains 

 would again return to their former domain, increased by refugees from the 

 circumpolar continent of temperate climate, driven southward by the increas- 

 ing cold. 



"Such being the case, it ought to be possible, with well-prepared lists of the 

 insects of the plains and mountain regions, by comparison with lists of the 

 local fauna of other zoological districts of the continent, to ascertain, with 

 reasonable probability, the invasions from different directions by which, In the 

 first place, the newly emerged land was colonized; and, in the second place. 



