NEPTICULA BASIGUTTELLA. 219 



disc of the wing is strong and rather smooth, but not so glossy as in 

 X. tiliae (Heinemann). 



EGG-LAYING. The egg is always laid on the upperside of an oak- 

 leaf, by the side of a large vein, or in the angle between two 

 veins. Nolcken says he has never found an egg on the surface of the 

 leaf away from a rib. He further writes : " The egg is not pushed 

 under the epidermis, but glued upon the outside of the leaf. It forms 

 an elliptical, more or less pearly, shining pustula, thickly covered with 

 a white shiny gum, by which it is fastened to the leaf." 



MINE. The mine is almost of the colour of the oak leaf in which 

 it is placed, and hence is difficult of detection. In the mine the frass 

 is coiled, the pellets being arranged in superimposed, slightly curved, 

 rows, which run across the mine with the nicest precision. Heinemann 

 writes : " The mine forms a long, rather tortuous gallery of nearly 

 uniform width, entirely filled up with dark green excrement." 

 Nolcken describes the mine as being " very long, gradually increasing 

 in width, with many convolutions, and extending over a large part of 

 a leaf, the flap from which the larvae finally escapes being on the 

 upperside, and resembling a horse-shoe in shape. The mine cannot 

 be seen from the underside of the leaf, and in its early stages is with 

 difficulty detected on the upperside, since the excrement is then 

 greenish, and only becomes blacker later in the insect's life. In dried 

 leaves, the commencement of the mine, seen from above, appears to be 

 of a pale, dirty, yellowish-green colour, without a distinct frass-line. 

 This latter becomes suddenly visible, probably after a moult. Held 

 against the light, the whole of the mine appears, from its commence- 

 ment onwards, to be entirely filled up with green, and later, with darker 

 green (almost blackish-green) frass, so that only a very narrow, pale 

 margin exists on either side of the frass-line, until towards the end of 

 the mine, when the margins become broader and more distinct. In the 

 first part of the mine the frass-line exists as a somewhat interrupted, 

 fine, uniformly coloured dark thread. It then presents the appearance of 

 lighter and darker spots, usually with the darker frass lying along the 

 margins. Owing to the movement of the larva in its gallery whilst 

 eating, the frass is deposited transversely, sometimes irregularly, but 

 at others forming a series of zigzag lines, where the frass is deposited 

 in a series of short curves. It would appear as though the climatic 

 conditions (whether wet or dry at the time of its formation) influence 

 the character of the frass-line." 



COMPARISON OF THE MINE AND LARVA OF N. BASIGUTTELLA WITH THOSE 

 OF THE ALLIED SPECIES. The mines of uY. samiatella, X. mjicajntella 

 and X. atricapitella differ in the following characters from that of 

 A r . basiyuttella. Their mines are broader, the frass-line usually runs 

 as a narrow, strikingly blackish thread along their middle, leaving 

 very wide, conspicuous, whitish margins on either side, the margins 

 being double the width of the thread. In many mines (often only in 

 places) the frass-line becomes granular, consisting of scattered pellets, 

 and broader than usual, but even then paler areas and the light 

 margins remain, and are much broader than in the mine of X. basi- 

 ffiittella, whilst the whole of the leaf cuticle affected by the mine is 

 more strikingly coloured, whitish or brownish. In addition; X. basi- 

 guttella has a green larva, whilst those of the other named species are 

 yellow, with a reddish-brown intestinal canal. X. subbimaculella (ac- 



