(ILACIAL REMINDERS. 589 



The nio.st striking feature in their occurrence is the fact tliat the genera 

 into which these two butterflies fall have an altogether 8})ecial interest of 

 great significance in this connection ; for they are exclusively or very 

 largely arctic, and there are but three other such genera known in the 

 whole butterfly world. These others are Erebia, of which there are some 

 examples in subarctic America and in the Rocky jMountains ; Agriades, 

 which comes no nearer to us than Labrador, and is found affain in the 

 high mountains of the western half of our continent ; and Eurymus, 

 which is less exclusively arctic than the others, having representatives also 

 over almost the entire globe, excepting in tropical countries, and of which 

 we have three species in New England, one of them subarctic. Oeneis, the 

 genus to which one of our Mount AVashington forms belongs, occurs else- 

 where only in high mountain regions, and, with but one or two exceptions, 

 beyond forest limits, whether toward the pole or the zenith. Several 

 species occur among the mountains of our west, one is found in the Alps 

 of Switzerland, and one in the Himalayas. Brcnthis, however, the other 

 White Mountain genus, Avhile occurring as far north as buttei-flies are 

 known (tAvo or three species having been found by the very shores of the 

 Arctic Ocean, in Greenland and Grinnell Land), is represented more 

 largely by species occurring in tlie temperate zone, and we have in New 

 England itself two of such species. In keeping Avith this distribution of 

 these genera, the White iMountain Oeneis is not only confined to the bar- 

 ren summits of the range, but even, as we have found, to the higher parts 

 of this region, although its food plant, Carex, is found everywhere 

 below the forest. The White ^fountain Brenthis, on the other hand, 

 rarely or never occurs in the same district with Oeneis, being almost 

 wholly confined to the lower half of the barren region. Its food plant, 

 though not known, is presumed to be violets, Avhich are found in scanty 

 numbers in the strictly alpine district, a single species being found in 

 favorable spots ; but they are sufficiently abundant in the subalpine zone. 



These two butterflies, then, may be looked upon as the oldest inhabi- 

 tants of New England, which followed the retreating ice sheet in its pro- 

 gress northward, and whose brethren, thought by some to be even forms 

 of the same species, still cling to the borders of the ice region of the 

 north. They were the first of their tribe to fly over the barren fields of 

 New England when the earliest verdure began to follow the withdrawing 

 ice, and moving with it step by step, Avere at last, some of them, beguiled 

 by the local glaciers which remained in the White Mountain region long after 

 the main glacial sheet had left these mountains far in its rear, and until 

 connection with the main body was finally cut off. As one of our writers 

 has expressed it : " Return became at length impossible. They advanced 

 behind the deceiving local glaciers step by step, up the mountain side, 

 pushed up from below by the warm climate, which to them was inicon- 



