286 BRITISH LEPIDOPTEBA. 



by the shorter antennae and wings ; the larger and whiter eye-caps, the 

 forms of the fascia, partly also by the want of the dark bordering of 

 the fascia towards the base. Besides, N. alutinomc has more blue on 

 the disc, especially beyond the fascia, and the fascia is narrow, more 

 defined, and not expanded on the inner margin, whilst before the 

 fascia the anterior wings are irrorated with dark violet (Heinemann). 



EGG-LAYING. The egg is laid on the underside of a leaf of birch 

 (Nolcken). 



MINE. Heinemann describes the mine as being " long, slightly 

 tortuous, generally abruptly angulated, and with a slender excremental 

 line/' Wood says that the mine is small, nearly filled with irregularly 

 arranged frass, and is similar to that of N. betulicola, but, in a general 

 way, the gallery is almost completely filled with frass in the mine of 

 N. luteella, and about half-filled in that of N. betulicola. Wood 

 writes : " In the typical mine of X. luteella, the frass is distributed 

 without any attempt at order, and fills the narrow gallery to about 

 three-fourths of its width, but not unfrequently late in the autumn, 

 when the leaves have lost much of their nutritive qualities and the 

 indigestible cellulose has increased, the frass becomes so bulky that 

 it now almost fills the mine, and is, at the same time, deposited coil 

 fashion, though in a slovenly tentative sort of way, as if the larva were 

 unused to the practice." 



COMPARISON OF MINES OF N. LUTEELLA AND N. BETULICOLA. It is a 

 difficult matter to distinguish between the mines of N. luteella and 

 N. betulicola. The relative breadth of the frass-track (about half- 

 filling the mine in N. betulicola, and almost completely so in luteella) 

 ought to serve to differentiate them nicely, but then, under certain 

 conditions, each varies so in the direction of the other, that it would 

 bo rash sometimes to say to which of them a mine belonged. There 

 are other small points of difference, but I need not particularise them, 

 since they, too, are liable to variation, and it is not after all a very 

 important matter to distinguish the empty mines, so long as we can 

 recognise the full ones. Besides varying in the direction of N. betuli- 

 cola, X. luteella also occasionally mimics the mine of X. (linthii/uoiila 

 by a rough attempt at coiling, but so clumsy is the counterfeit that it 

 ought never to deceive the collector (Wood). 



LARVA. Heinemann describes the larva as "pale green, with 

 darker dorsal line, and feeds in July and October, in birch leaves." 

 Wood observes that " the larva mines with the back up, but shows 

 neither cephalic ganglia nor ventral cord. It is yellow in colour with 

 a pale brown head, and no other visible markings, although, out of 

 the mine, the larva shows the urinary ducts, which are not 

 dark enough to be seen when it is in the mine." Nolcken writes : 

 " Die Raupe war blass honiggelb mit blass braunen Kopfe, Darm kaum 

 in der Hinterhalfte stellenweise durchscheinend, schmutzig dunkel- 

 griinlich braun, Keulenflecke fast nicht sichtbar." Nolcken further 

 draws attention to the colour that Heinemann gives to the larva of 

 this species. 



COCOON. The cocoons (4) average 2-5 mm. long, and 1-5 mm. 

 wide. In colour they most resemble that of the cocoons of X. 

 (listhif/uenda, being of a pale flesh-colour when fresh, but becoming 

 darker, duller, and more ochreous when they have been exposed to the 

 weather. The cocoon is roughly ovate in outline, with no lateral 



