27 
is certainly well worth separating as a species, a manifest convenience 
for the working out of its variation, since no single specimen is like 
any single specimen of hastata ; yet there can be no question about its 
very close resemblance to its more widely distributed relative, of which 
it is simply the Iceland representative. Its larva feeds on the dwarf 
birch of that country, also, nearly as commonly, on I 'actinium and 
occasionally on sallow (Staudinger, Stctt. Ent. Zeit., xviii., p. 261)— 
i.e., the same plants as its relative R. hastata var. subhastata (see infra) 
—and has apparently never been differentiated more definitely than by 
small colour-distinctions from that of hastata (vide Stgr., Inc. cit.; 
Mill., Icon., iii., p. 266, pi. 131, fig. 4-6). The chief characteristics of 
R. thulearia are its browner tone and peculiar t/reast/ appearance, so 
different, even in the best-marked forms, from the charming purity of 
the white and black of hastata, and the regular continuity of the 
subterminal, with consequent suppression of the sagittate markings in 
the marginal area, which, in some form or other, seem to be always 
indicated in hastata. Usually the subterminal line is quite orthodox 
in thulearia, but very occasionally a thickening between veins 3 and 
4, or even an increase of the white uniting this to the white band 
suggests the line of evolution of the missing mark. I have a long and 
variable series of thulearia obtained from the Eev. TI. H. Slater, 
unfortunately not mostly in the best of condition, owing chiefly to the 
difficulty which he had in accommodating insects during a rough 
ornithological campaign. I think the only named variety or aberration 
is var. idandica Gumpp. (Nora Acta, liv., p. 304, 1890) “ Strigis 
transversalibus et ciliis niveis, ceterum unicolori-infumata.” But to 
this is immediately added an “ ab.” unnamed, but with a brief 
diagnosis which I will quote. I propose for this extreme form the 
name ab. infumata mihi, n. ab. “ Alis infumatis, strigis, obsoletis.” 
In order to get at Gumppenberg’s meaning it must be understood 
that the type form of thulearia is “ nigricans, linea undulata et strigis 
duplicibus, albidis, infumatis, harum posteriore sinuata, non cum 
undulata cuhrerens ” (Herrich-Schaffer), so that the deviation in 
islanclica seems to reside chiefly in the purer white bands, while 
infumata represents just the opposite extreme. Obviously “ var.,” in 
the case of idandica, should read “ ab.,” and Gumppenberg must 
have got into some muddle (as usual!) in choosing such a name ; for 
the type form itself belongs to Iceland alone, as he duly recognises. 
To be sure, there appears to be some local variation, for Staudinger 
(Stett. Ent. Zeit., xviii., p. 259) says that northern examples are on 
the average much larger and whiter than southern; but it is rather 
absurd to single out either of them for a varietal name derived from 
that of the land which gives birth to them both. Nevertheless, of 
course the name will have to stand. Milliere (Icon., iii., pi. 131, lig. 6) 
has figured this rather extreme form, ab. idandica, which approaches 
hastata as nearly as seems possible with this species. Ab. infumata 
is also alluded to by both Milliere (tom. cit.) and in Staudinger’s 
interesting paper already twice cited (and which devotes lour pages to 
thulearia), being given in the latter as “ var. alis concoloribus nigri- 
cantibus $ $ ” ; it has never been figured, but you will find it 
represented in my series. A still more striking aberration than either 
of these, and apparently a much rarer one, is:— 
Ab. clara mihi, n. ab. The whole outer area of all the wings 
