THE SWISS SPECIES OF THE GENUS HESPERIA. 81 
particular aberration is a little larger than the type, the ground colour 
underside hindwing is of the fine reddish tone characteristic of fritil- 
lum, and the nervures of the same colour stand out very con- 
spicuously. In these three respects then, size, coloration, and 
prominent nervures, this aberration is remarkably like fritillum, but 
the white markings on the upperside will always enable it to be 
identified. The white spots on the forewing of armoricanus, although 
sometimes a little enlarged, never approach the heavy square markings 
of fritillim, and the intradiscoidal spot, although rarely rectilinear, 
never assumes the solid proportions of the well known “signe de 
Delahaye.”” Further, the amount of white on the hindwing is rarely 
(if ever) developed to the extent it is in fritellum. The latter is also 
a squarer insect in build. This form can be found in both broods of 
armoricanus; but, of course, it will only be in the case of those 
exawiples taken in the second brood that any question as to their 
identity can arise. 
The general likeness between the type forms of armoricanus and 
alveus has been already commented on. The two species occur to- 
gether at Follaterre. With a series of each side by side, they are 
separable at a glance; but if a single specimen of either is taken it is 
not so easy. ‘The date, when considered in connection with the con- 
dition of the specimen, is, however, an excellent means of identification. 
The second brood of armoricanus appears in late August and Septem. 
ber; the earliest date on which I have taken it being August 20th, 
and by this date alveus is very nearly over. I have taken both species 
together on August 22nd, armoricanus in numbers and quite fresh, 
and a few worn alveus, which made a quite unmistakable contrast. 
Occasionally, a retarded specimen of alveus will be met with in very 
fine condition ; and in such cases the collector (unless he employs the 
genitalia) will have to depend on the characters previously mentioned. 
In one respect, size, the difference is much more marked than one 
would be led to suppose by a comparison of measurements of a series 
of each species. If a specimen of alveus is seen on the wing among a 
number of armoricanus it immediately catches the eye as being some- 
thing different. .I have thus on several occasions picked out an alveus 
while it was flying among a number of armoricanus. I am inclined to 
say that nine times out of ten size alone will be sufficient to determine 
the species; for Nature in this instance comes to the help of the col- 
lector. It isa well known fact, that in many species of butterflies 
that are double-brooded, the individuals of the first brood are larger 
than those of the second ; and although there is no constant difference 
in size between the individuals of the two broods of armoricanus, yet 
there is a strong tendency to an increase in size (aberrationally) in the 
first brood. Such specimens, although still quite characteristic of 
armoricanus, might in the second brood be difficult to separate from 
alveus; but, occurring with the first, there is hardly any question as 
to their identity. Further, as already noted, a small specimen of 
alveus is an extreme rarity. 
Before leaving the subject of the distinguishing features of armori- 
canus and alveus, 16 must be noted that the prominence or otherwise of 
the nervures, on the underside of the hindwing, which is supposed to 
be a valuable character, is quite unreliable ; these nervures often being 
as pronounced in alveus as in any example of armoricanus. 
