IN THE BRITISH ISLANDS. 21 



varies much, the central stem sometimes being carried through very 

 far, at others not at all, making a mark shaped thus, V. Thirdly, a 

 point to which I have previously drawn attention, the variation in 

 position, and the frequent coalescing of the reniform and the orbicular. 

 Lastly, I would draw attention to the following remarkable fact, that 

 all those specimens which he selected to give me of the bidens variety, 

 also had the area outside the elbowed line, and between that and the 

 subterminal line shaded as in var. virga of tridens, but, I must add, 

 this banded character was not confined to the bidens form in his own 

 series, some specimens being banded, which possessed a normal basal 

 mark. There is also another remarkable fact about bidens. The 

 shoulder line in bidens passes directly to the costa, forming an 

 oblique, almost straight line, and is not angulated, as in typical psi, 

 towards its upper part, and bent back towards the base before reaching 

 the costa. The hind wings, too, are paler than psi. It will be noticed 

 (as Dr. Chapman pointed out to me) that bidens in all these respects 

 resembles menyanthidis rather than psi. Returning now to psi (as 

 apart from var. bidens), I would call attention to the fact that the 

 black longitudinal basal line rarely has a double bifurcation in psi 

 (although common in tridens), owing to the generally ill-developed 

 condition of the outer striga of the double transverse basal line, of 

 which the bifurcations are really a part. There never appears to 

 be in psi a duplication of the short transverse line (situated towards 

 the upper part of the elbowed line, above the ^-like mark), which is 

 of common occurrence in the allied species, tridens. A very large pro- 

 portion of our specimens in the London district have a very dark grey 

 ground colour, whilst in other districts the ground colour is very 

 white, and in others particularly ashy, almost with a faint slaty hue. 



a. var. virga, mihi. With the area directly outside the transverse 

 angulated (shoulder) line, of a darker shade than the ground colour, 

 giving an appearance of a transverse band. 



J3. var. juncta, mihi. With the orbicular and reniform joined on 

 their inner margins as in var. juncta of the allied species tridens. 



y. var. bivirgce, mihi. The anterior wings darker than in the type, 

 the space between the hind margin and the transverse line containing 

 the ^-like mark completely suffused with black scales; the basal 

 part of the wing also completely suffused, so that the insect has the 

 appearance of two bands crossing these wings. This beautiful variety 

 was captured on the racecourse at York by Mr. J. T. Carrington, and 

 is now in the collection of the late Mr. Sidebotham. 



8. var. su/usa, mihi. The whole of the ground colour is much 

 suffused with dark scales, giving the insect a very dark appearance. 

 The posterior wings are also much darker than in the type in both 

 sexes. This is the form generally, if not always, taken in the London 

 district, and occasionally found in most of the woods within a few 

 miles of the metropolis. I have never taken the pale type in my own 

 district (Blackheath), although it is common enough in Darenth, Chat- 

 tenden, and other woods only a few miles off, in which the var. su/usa 

 is rarely seen. 



e. var. cuspis, Stephens (non Hb.). There is a continental species 

 of this name closely allied to A. psi, which species (cuspis, Hb.) 



