Review of the Genus Erebia. 235 
on the Alps of Central Europe, and, except one or two 
species in the Pyrenees, have no wider range. Two, 
three, or more of the species are often, indeed usually, 
associated on the same ground; yet, in spite of what 
has been advanced as to their crossing and present- 
ing intermediate forms, the evidence of the clasps is 
quite to the contrary, especially since the species said to 
be mixed are those that are most distinct. But all these 
species are sufficiently closely allied to lead us to conclude 
that they have a common origin; and they therefore 
compel us to accept in explanation Romanes’s theory of 
physiological isolation to account for their origin and pre- 
servation as distinct species. We have then in the grass 
Erebias a number of very similar and associated forms with 
very definitely distinct appendages; whilst in the other 
series of species, when geographical isolation has been 
chiefly at work, we have slightly different forms with 
identical appendages that compel us to regard them as one 
species, 
We further find that many species have dark or black 
forms:—glacialis, pluto; fasciata, magdalina; nerine, melas; 
manto, cecilia ; whilst wme, mnestra, epiphron, stygne, and 
_ others have forms making a very close approach to these. 
Li. lefebvrei has its coloured and dark forms, and £. cecilia 
from the Pyrenees, which appears to require a fresh name, 
is the only dark form not correlated with a normal coloured 
type. 
EXPLANATION OF PLATES V—XVI.« 
The figures are all sketched under the camera lucida, the amplifi- 
cation being 16 diameters. 
Ailowing for some roughness in the sketches, the general form of 
the processes of the tegumen and of the clasps, and the arrangement 
of the spines or styles are quite accurate, 
The view of the clasps is usually lateral, but in some instances a 
more vertical aspect is given, to illustrate the form of the clasp. In 
a few cases the clasps are flattened by pressure, so that they look 
broader than they actually are. This gives, however, a more 
accurate single view of the form of the chitin, but many clasps do 
not admit of it. 
