ENTOMOLOGY OF COLORADO. 321 



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 obscures the facts, and leads us to ignore one of the 

 most interesting phenomena that are presented to a zoologist. 



I was very well pleased to find these opinions shared by so acute 

 an observer as Mr. Thos. E. Bean, of Laggan, Alberta. He wrote 

 me on Dec. 6, 1892 : " In answer to your query, I can say most de- 

 cidedly that in my opinion the butterflies of this [LagganJ district 

 may be arranged in two categories as to their age as species : one set 

 of apparently old old forms, the others having the appearance of being 

 forms now taking character. I have now under consideration one of 

 the latter kind, a Colias, which, if completer study confirms my 

 present views, I shall probably announce as a distinct species. In 

 that case I may give it the name post-glacialis, in accordance with 

 the idea that it is one of these recently separated species which have 

 not yet acquired complete equilibrium of characters." 



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. Of the forty-six genera of 

 aculeate Hymenoptera in the niid-alj)ine of Custer County, thirty- 

 three, or about two-thirds, are also found in the British Is. This is 

 not very different from what might be expected ; but the further wide 

 distribution of some of these genera is shown when I open the volume 

 of the " Zoological Record" for 1889, which happens to be at hand, and 

 find references to Megachile from the Congo, Andrena from Sicily, 

 Trypoxylon from Panama, Ammophila from Afghanistan, and so forth. 



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

 equally productive of species over their whole areas. Dr. Simroth 

 has pointed out how in the case of the slug-genus Agrlolimax, one 

 or two species range almost unchanged over an immense territory ; 

 while in the Mediterranean region and the country eastward of it, 

 species are produced in abundance. Dr. A. R. Wallace refers 

 (" Island Life," ed. 2, p. 368) to the existence of four or five peculiar 

 species of the moss-genus Mnium in the Drontheim Mountains in 

 central Norway ; these are " found nowhere else, although the genus 

 extends over Europe, India, and the southern hemisphere, but always 

 represented by a very few wide-ranging species except in this one 

 mountain group!" Among flowering plants good instances can 



TRANS. AM. ENT. see. XX. (41) NOVEMBER. 1893. 



