54 
The spring and summer broods present generally a well-marked 
difference, especially in the male, the spring specimens being light, 
with very little, if any, brown border, while the summer specimens are 
usually strongly marked. While on this subject I must mention, to 
prove the rule in the proverbial manner, that the darkest male in my 
series, with the exception of one very extreme form of the ab. li/llns, 
Esp., was captured on June 22nd, 1902, and therefore belongs to the 
spring brood. The specimen referred to is a fine male of the ab. 
bipiipillata, Cosm., and was taken at Wimbledon.* 
The variation of this species, apart from seasonal dimorphism, 
may be considered under three heads:— 
Variation in ground colour. 
Variation in the direction of increase of marking. 
Variation in the direction of decrease of marking. 
I. Variation of Ground Colour. 
This is very extensive, and series from different districts often show 
considerable difference. Pale specimens are not at all infrequent in 
some localities and perhaps occur more frequently in some seasons than 
in others. One hesitates to dogmatise from insufficent data, but may 
perhaps suggest that in fine, hot summers the paler forms are more 
abundant; in dull, wet summers the darker forms. This has been one’s own 
experience, and one is inclined to regard it as more than a coincidence. 
This suggestion of course only relates to the around colour, not mark¬ 
ing, and only to the slight variation in colour such as one would not 
become aware of, except by the comparison of long series from various 
localities, and extending over a long period of collection. Extreme 
forms must be regarded as sporadic and are rare. A well-known 
yellowish variety has been made ab. pallida by Tutt, and there is an 
excellent figure of it in Moseley’s “ Varieties.” 
An exceedingly rare variety has the usual tawny ground colour 
replaced by white. Such a specimen was in the “ Maddison ” 
collection, and others exist, but it must be very scarce. I am not 
aware that this form has ever received an aberrational name. If 
this is so, it must be almost unique among striking varieties of British 
Lepidoptera. No doubt the obvious name, “alba” will sooner or 
later be applied to it by some systematist. 
On the other hand, the colour may be darkened to a brownish- 
tawny. I have a specimen of this form taken in 1910 at Westerham, 
in Kent (exhibited), which is further remarkable in having a small 
spot near the anal angle of the hindwing (upperside), an unusual 
form of variation in this country. This brownish-tawny form, again, 
is possibly local or seasonal; a long series of it from, I believe, 
Delatnere Forest, was in the collection of the late Mr. Harrison, of 
Woodford. 
More extreme forms also occur, and specimens have been recorded 
* Since the above was written I have collected a short series at Wimbledon. 
This year (1913) the spring specimens were larger, of a deeper ground colour, and 
more strongly marked, than the summer specimens. I exhibited the series before 
this Society on October 21st, 1913. 
xxii.-xxiii. 
