370 



Insects. 



the cervical tuft luteous, the larger eye-caps are pale yellow, with a 

 silvery gloss. The antennae in both sexes have less than half the 

 length of the anterior wings ; they are blackish ; the abdomen is black- 

 gray, with metallic lustre ; the legs are blackish, in certain directions 

 with a silvery gray lustre ; the middle tibiae and tarsi, as also the ends 

 of the posterior tarsi, are whitish. The anterior wings are proportion- 

 ally broad, rounded at the tip, though this form is rather variable ; 

 the ground colour is not, as Frey says, black with a violet gloss, but a 

 mixture of bronze and blackish gray, rather smooth, with tolerably 

 decided metallic lustre ; beyond the fascia it is violet, more rarely 

 blue. The fascia itself is very posteriorly placed, at more than two- 

 thirds of the length of the wing, scarcely oblique ; it is rather narrow, 

 of uniform width, distinctly but not sharply outlined, white with a sil- 

 very gloss, sometimes inclining to golden, especially in the female. 

 The cilia are violet-gray at their bases, with the tips whitish gray ; at 

 the anal angle they are rather darker. The posterior wings and their 

 cilia are gray. Beneath all the wings are fuscous, the anterior rather 

 the darker. 



This species is most nearly allied to N. plagicolella, and is sometimes 

 very difficult to distinguish from it, but the latter has the frontal tuft 

 much brighter ferruginous and the antennae are longer, reaching in the 

 female to the middle of the anterior wings, and in the male perceptibly 

 beyond the middle ; besides, in N. plagicolella the ground colour of 

 the anterior wings is more bronze, paler and more glossy, and not so 

 inclined to black-gray ; before the fascia there is a more decided violet 

 tinge ; the base, on the other hand, is always rather paler dull bronze- 

 colour ; the fascia is close beyond the middle of the wing, rarely as 

 narrow as in N. betulicola, and has a more decided metallic lustre ; 

 the cilia are decidedly of a darker gray. Moreover in N. plagicolella 

 the middle tibiae are not paler than the other legs. N. raicrotheriella 

 may be distinguished by the narrower anterior wings suffused with 

 violet, and before the tip almost of a pure blue, by the narrow rather 

 oblique fascia, and by the darter gray cilia. N. luteella has the disk 

 of the anterior wings less smooth and dull, the fascia is not placed so 

 posteriorly, and perceptibly expands on the inner margin, inclining 

 to yellowish with very slight glossiness. 



The amber-yellow larva with green dorsal vessel feeds in July, as 

 also at the end of September and beginning of October, in the leaves 

 of Betula alba ; I counted twenty-five specimens in one leaf. The 

 mine is rather broad, tortuous, with a loose excremental track in -the 



