284 . BRITISH LEPIDOPTERA. 



on the inner margin near the base ; just beyond the middle is a rather 

 oblique, slender, very brilliant, silvery fascia ; tip of the wing purplish- 

 black ; cilia fuscous, with the extreme edge whitish. Posterior wings 

 and cilia grey. 



COMPAKISON OF N. ALNETELLA WITH N. AURELLA AND N. MARGINI- 



COLELLA. X. alnetella may be distinguished from N. aurclla by the 

 absence of any indication of a purple fascia before the silvery one, 

 and by the paler golden colour at the base of the inner margin. These 

 two last characters also serve to distinguish it from X. mar;/inic<>ldla, 

 which is sometimes but little larger than N. alnetella, and, besides, the 

 fascia, in the latter, is also more oblique (Stainton). 



EGG-LAYING. The egg is laid on the underside of an alder leaf, 

 close to one of the lateral ribs. 



MINE. The mine forms a long", slender gallery, very wavy and 

 irregular, the excrement forming a central blackish line, and is similar 

 in character throughout, except that it gradually becomes broader as 

 the larva increases in size. 



LARVA. The full-grown larva resembles somewhat that of X. 

 microtJteriella. Its length is nearly 2 lines; colour pale amber-yellow, 

 with the dorsal vessel green, anteriorly whitish ; the head pale brown, 

 with the mouth and two slender lines receding from it dark brown ; 

 the supposed renal organs showing as two brown serpentine viscera. 

 Nolcken writes : " Die Eaupe ist hellgelb, der Kopf sehr blass braunlich, 

 Keulenflecke klein, grau, undeutlich, meist unter den Riindern des 

 Kopfes verborgen ; sie verliisst die Mine durch die untere Blattseite." 



COCOON. The cocoons (3) average 2-5 mm. in length and 1-8 mm. 

 in width. They are roughly almond-shaped one end being consider- 

 ably narrower, the other wider and rounded on the margin. The 

 raised surface rises regularly from the edge of the cocoon, and becomes 

 highest at the narrow end. The pupa emerges from the broader end. 

 The colour of the cocoon is dark red-brown, the surface rough, with 

 the ends of silken fibres projecting roughly and irregularly all over 

 the surface. The empty pupa-case is exceedingly transparent (more 

 transparent than is usual, even in this group), the skin looking just 

 like a delicate film and showing slight iridescence. [Described June 

 15th, 1898, under a two- thirds lens, from cocoons sent by Dr. Wood.] 

 Stainton says : " The cocoon resembles that of X. salicis, and is 

 spun up on the surface of the ground." Nolcken notes: " Cocon 

 heller oder dunkler braunlich ochergelb, ziemlich flach birnformig, 

 manchmal elliptisch." 



FOOD-PLANT. Alnus glutinosa. 



TIME OF APPEARANCE. Probably double-brooded. The imagines 

 appear in May and early June from mines of the preceding September- 

 October. Imagines are also to be obtained in July, probably from 

 June larvae. Bower captured imagines on July 18th, 1892, by 

 sweeping alder trees at Eltham ; whilst Stainton bred imagines April 

 29th, 1855, from Beckenham larvae, May 6th, 1855, from Darlington 

 larvae, June 24th and July 7th, 1858, from Beckenham, June 8rd- 

 6th, 1857, from Beigate larvae. Threlfall bred imagines in June, from 

 larvae obtained at Windermere, Sept. 20th, 1880. Stainton found 

 mines on October 15th-22nd, 1854, at Beckenham ; Law, on October 

 18th, 1854, at Darlington ; Bower, on October 19th, 1892, October 

 6th, 1894, September llth, 1895, October 21st, 1897, at Eltham ; 



