ECOLOGY OF ISLE ROYALE. 167 



all the strictly endemic element in the Rocky Mountains is of post-glacial 

 origin — that is, according to the views here set forth. This means a good deal, 

 if it is actually the case, as I believe. Under certain circumstances, species 

 develop quickly, and we have, at least among insects and flowering plants, a 

 great array of new species coming into existence. Such species are closely al- 

 lied to species from, which they sprang, and to each other, so as to give rise 

 to much dispute as to their validity — as an example, one may cite the genus 

 Argynnis, which has been very productive of post-glacial species in America. 

 In such a case it matters little whether we term all these diverse forms true 

 species, or subspecies or races, — but to lump them under a common name ob- 

 scures the facts, and leads us to Ignore one of the most interesting phenomena 

 that are presented to a zoologist, pp. 320-321. 



"Species-Forming Areas. It is well known that the genera commonly accepted 

 are unequal in value, but most of those whose validity could not be questioned, 

 are evidently of considerable antiquity. 



"But the curious thing is, that these wide-ranging genera are not equally 

 productive of species over their whole areas, p. 321. 



"Among insects, Argynnis and CoUas, and several genera of Noctuae, exhibit 

 strong species-forming tendencies in the Western States of North America. 

 Catocala, in the Eastern States, has a very strong species-forming area. And 

 so on in many other instances which will occur to the reader. This phenomenon 

 is a most remarkable one, since it affects chiefly old and almost cosmopolitan 

 genera, and does not occur in the same districts in all the genera. Two cosmo- 

 politan genera, as we have seen, may have their species-forming areas on op- 

 posite sides of the world. It would seem, indeed, as if there were causes at 

 the bottom of it, that we do not yet understand." p. 322. 



Fall, H. G. and Cockerell, T. D. A. 1907. pp. 150-151, 152-153: "Comparing 

 the beetles of New Mexico with those of Colorado, one is struck by the large 

 amount of difference in the lists. Colorado has not, of course, the important 

 and characteristic Middle Sonoran element, but the higher elevations are con- 

 tinuous from north to south, and one would exi>ect a practically identical fauna. 

 Botanical investigations, however, have revealed striking differences in the 

 plants of the northern and southern Rocky Mountains, and a degree of en- 

 ■demicity among those inhabiting the mountain ranges which is quite surprising. 

 The oaks (Quercus) are abundant in New Mexico, and have a luxuriant develop- 

 ment as far north as Manitou, Colorado, and even beyond. But at Boulder, and 

 north of Denver, generally, they are totally absent. On the western slope they 

 go farther north, and one species just enters Wyoming; but there are none^ 

 at all in Wyoming, with this exception, and none in Montana. This alone would 

 explain the northward limitations to the distribution of the numerous species 

 of Coleoptera which are attached to the oak, and various similar cases could 

 be cited. It appears probable that the oaks were driven south during the 

 glacial period, and owing to the unsuitability of their seed for being carried 

 great distances, have been unable to recover their lost ground. Under these 

 circumstances, the ample powers of flight of certain of the oak feeding beetles 

 are of no service for promoting migration northward of the slowly moving 

 line of oaks. pp. 150-151. 



"It will be noted that New Mexico shows a greater proportion of non-Colorado 

 genera than species; or, in other words, the species found in New Mexico but 

 not in Colorado are more likely to be of non-Colorado genera than in the 

 reverse case. This is explained by the fact that the desert fauna in nearly all 

 groups is rich in peculiar genera, but these are represented so far up as New 

 Mexico by comparatively few species. On the other hand, the boreal fauna, 

 -so strongly developed in Colorado, is largely characterized by the abundance 

 of species of circumpolar genera. 



"In Colorado the eastern plains region has been little searched for beetles, 

 and the corresponding region of New Mexico is also poorly known. There is 

 no doubt that the plains will furnish many species additional to the lists, and 

 most of these will doubtless be common to both. The following are characteristic 

 eastern species which are known to reach New Mexico, but have not yet been 

 found in Colorado: Searites subterraneus, Clivina bipustulata, Clivina ferrea, 

 Aspidoglossa subangulata, Panagaeus fasciatus, Tachys xanthopus, Pterostichus 

 sayi, Bynastes tityus, Anomala undulata, Alindria teres. 



"The New Mexico list contains over 135 species, indicating that the eastern 



