168 MICHIGAN SURVEY, 1908. 



fauna is really crossing the plains to some extent, and not only reaching^ us by 

 way of the northern mountains. There are strong reasons for believing that 

 a considerable part of this migration is recent, and has been assisted involun- 

 tarily by man. This affords, of course, a strong argument in favor of the- 

 speedy exploration of western regions, in order that their original fauna may 

 be ascertained before it is unduly contaminated by introduced forms. Fortunate- 

 ly for the naturalists, the desert will not quickly or easily accommodate alien 

 elements, but it is quite otherwise in more ordinary localities; and as Perkins 

 has shown in the Hawaiian Islands the result may be destruction as well as 

 contusion. 



"The number of species common to New Mexico and Southern California, but 

 not known from Colorado, is over 160, indicating a wide-spread southwestern 

 fauna; but in general, th« species of the Southern California coast region are 

 not those of the Rocky Mountains. 



"We find over 30 names of New Mexico species listed from the Lower Rio 

 Grande, but not in the Colorado, Southern California or District of Columbia lists. 

 Such for example: Cincindela circumpicta, Cindela severa, DyscMrius ter- 

 minalis, Philopfiuga viridicoUis, Helluomorpha ferruginea, Oodes cupraeus, 

 Ischiodontus ferreus, Ludius texanus, Agrilus addendus, Mastinocerus texanus. 



"The following are examples of characteristic southern genera which reach 

 New Mexico, but do not enter Colorado: Thalpius, Hololepta, Sandalus, Thrin- 

 copyge, Lycus, Plusiotis, Aphonides, Strategus, AllorMna, Deroirachus, Tylosis^ 

 Dendroiias. 



"Because of the conspicuous place which these southern genera oc'"upv in 

 the fauna, an entomologist arriving from the north or east is very likely to 

 assume that the Middle Sonoran of New Mexico contains precisely the same 

 elements as the Lower Sonoran of Arizona just as it has been assumed that 

 Florida is typically West Indian, because its numerous West Indian genera 

 attract attention, and the absence of innumerable West Indian types is not sO' 

 readily observed." pp. 151-153. 



Hamilton. '94 a. pp. 408-415. Cf. also Fauvel '89. Hamilton gives the fol- 

 lowing lists of species indicative as to their nativity: 



1. Species equally native in North America and in northern Asia not yet 

 observed as occurring in Europe — 49 species. 



2. Species native in North America and Northern Asia occurring inxEurope — 

 277 species. 



3. Species native in North America and Europe not at present known to 

 occur in northern Asia — 50 species. 



4. Species probably introduced into North America now acclimated occurring 

 in Europe, and those marked with a * likewise in Asia. Many of these are 

 cosmopolite, or becoming so, through commerce — 216 species. 



5. Species cosmopolite or subcosmopolite. 



Horn. G. H. 1872. pp. 383-384. "As is well knovm to all collectors, various 

 species of Eleodes occur in great numbers in all parts of the west of our con- 

 tinent, and the species themselves occur over a wide range of territory, and 

 are not limited, as might be inferred from their apterous condition, to regions 

 of small extent. As we pass from east to west over a given line, we find 

 variations of average temperature, and of course great differences in altitude. 

 These two causes, combined with, of course, the botanical changes, have tended 

 to produce variations from a given type to a greater or less extent. Eleodes 

 obscura Say affords a beautiful illustration of the extent to which this diver- 

 gence may be carried. As a general rule I find, not only in Eleodes, but also 

 in many other genera, that the higher the elevation or the colder the climate, 

 the rougher and more deeply sculptured Is the species. The smoother forms of 

 E. obscura may therefore be expected in the southern regions in which it occurs; 

 for example, var. dispersa is New Mexican, elytra with scarcely any traces 

 of striae; var. obscura, elytra distinctly sulcate, but. not deeply, is from Colorado 

 and Southern Idaho. As we advance to the west the elytra are more deeply 

 sulcate, as in var. arata, while var. sulcipennis, from nearer the Pacific Coast, 

 has deeply sulcate elytra, with very convex interspaces. The same variation 

 of sculpture occurs in Galosoma luxatum. Say, which starts in Colorado with 

 comparatively smooth elytra, until in Vancouver we find the elytra covered with 

 lines of granular elevation.5, forming the variety known as C. pemelioides. 

 Walker. The two extremes of each series above noted appear to differ widely 



