Ifc THE BRITISH ISLANDS. 



far as the differentiation of the species is concerned. Most of the 

 species are so polymorphic that it is often very difficult to distinguish 

 the various forms of the same species, and, added to this, we find that 

 many of the species are so closely allied, that it is almost impossible 

 even to distinguish some of the species from each other. This is 

 strikingly the case with regard to A. tritid, cursoria and obelisca. 

 There are, however, some very distinct species which it would be im- 

 possible to confound with other species. The genus shows, too, some 

 very striking cases of sexual variation ; the difference in the sexes of 

 A. puta and cinerea being very marked, the females of both these 

 species having been named by various authors as distinct species from 

 the males. In almost all the species, the females are darker than the 

 males, and this difference is especially noticeable in the hind wings. 

 With regard to the range of variation in the colouring of the fore wings, 

 probably vestigialis, puta, segetum, lunigera, corticea, cinerea, cursoria and 

 tritid exhibit an almost equal range, extending from specimens of the 

 very palest whitish-grey colour (in some of the males) to most intense 

 black in one (the female) or both sexes. It is remarkable, too, that a 

 form of pattern which is constant in one group, becomes an occasional 

 form of pattern in another. The group containing cursoria, tritid and 

 obelisca is probably the most difficult to name and understand of any 

 in the whole of the NOCTU^E. It has throughout, two well defined 

 forms : (1) with the anterior wings crossed by a number of transverse 

 lines, and no trace of longitudinal markings, (2) with the transverse 

 lines almost obsolete, being obliterated by the development of pale 

 longitudinal lines, especially along the areas of the costal and median 

 nervures. The former type without longitudinal lines is rare in our 

 British specimens of obelisca, although apparently common enough in 

 some European localities. In cursoria, on the other hand, this form 

 is the commoner, the longitudinally marked form being rarer (but still 

 not at all uncommon). It is worthy of notice that one species 

 ashworthii which has long been considered as purely British, has 

 recently been referred by Mr. Dobree to the more widely-distributed 

 Continental species known as candelarum, of which ashworthii is con- 

 sidered a melanochroic variety. I have previously mentioned that 

 the hind wings present different variations, and I may add that these 

 are worthy of study, but that no absolute reliance can be placed on the 

 colour of these as indicating the sexes, as it is often assumed may be 

 done. Whether or not some of the species of this group are really 

 distinct, is often questioned by lepidopterists, but there is only one 

 British species so-called aquilina which I am really inclined to 

 sink as a variety. Obeliaca and cursoria are distinct without doubt, 

 and niyricans, another species, about the specific distinctness of which 

 doubt has been expressed, is so abundantly distinct that one almost 

 wonders why doubt has ever been thrown on it, although it must be 

 admitted that some of the obscure forms of tritid bear considerable 

 superficial resemblance to certain forms of nigricans. Concerning the 

 specific distinctness of these species, an article of mine will be found 

 in the ' Entomologist,' vol. xxi., pp. 171-176 and 198-202 where the 

 matter is discussed at length. I have nothing to add to what is there 

 written, except that I am now more than ever convinced of the com- 

 plete distinctness as species of niyricans, tritid, cursoria, and obelisca, 

 and the certainty that aquilina is simply a variety of tritid. In dealing 



