Erebia palarica and Erchia stygnc. 18 



that the mean expanse of the two species differs by no less 

 than 11 mm., nearly half-an-inch. The smallest £ ranging 

 in size very close to stygne, var. hispanica, has a facies quite 

 characteristic of palarica, so that no one could confuse them 

 together. 



Palarica is indeed the largest of all the Erebias, averag- 

 ing 59'0 mm. in exrjanse, and ranging from 55 mm. to 

 64 mm. 



The largest Erebia according to Ruhl is parmmio, to 

 which he gives an expanse of 50 mm. to 55 mm. E. cydopius 

 is as large, and embla very nearly so. I find, however, 

 that evias goes to 54. mm., but this is a maximum. 

 Palarica has 59 mm. as an average. 



In size, stygnc, at Pajares, and palarica do not overlap ; 

 the largest of the one is smaller than the smallest of the 

 other. 



The next point, is that each was, wherever Ave closely 

 observed it, strictly confined to its own habitat, into which 

 the other did not trespass ; this was very remarkable at two 

 points where the areas occupied by each approached to 

 within a few dozen yards of each other. At one of these 

 places opportunity served for me to notice how sharply 

 defined was the margin of the territory of each species, and 

 how a specimen driven over the border, came back after a 

 very short detour. Nor did I ever find one butterfly where 

 I found the other though it might not be very far off. 



Still it is difficult to suppose, considering how common 

 they were in places, each in its own area, and how close 

 these areas often were, that specimens did not sometimes 

 visit the habitats of the other species, though I did not 

 meet with such a case. And if they did and they were 

 really all one species some crossing was to be expected, and 

 intermediate forms ought to have occurred. Yet I must 

 have seen many hundreds of specimens altogether of both 

 species. In most places there was some difficulty in taking 

 specimens, and sometimes only two or three were taken 

 out of a score seen, and of these taken, though many 

 wretched specimens were retained, a large number in poor 

 condition were discarded. Those brought home must 

 therefore be but a portion of the number of individuals from 

 which I draw conclusions. Yet there never was the 

 slightest difficulty in saying at once, of which species any 

 particular specimen was. There was no trace of interme- 

 diate or transitional forms or of hybrids. Considering how 



