1894.1 95 



The gallery-miners of the birch (Betula alba and glutinosa) . Six 

 species occur here, whilst I learn from Mr. ^Fletcher that a seventh is 

 found in Sussex, having a mine hard, perhaps impossible, to be dis- 

 tinguished from that of continuella, and a cocoon and imago extremely 

 like Jloslacfella. My own six are continuella, distinguenda, hetulicola, 

 luteella, lapponica, and an unknown one, which I have only lately 

 recognised as distinct by its mine and larva, but have not yet bred ; 

 I will call it for the present No. 1. They all lay on the under surface 

 of the leaves, and have yellow larvaa, excepting No. 1, which has a 

 greenish-white larva. As a first step towards differentiating them, 

 they might be broken up into three pairs in accordance with the three 

 types of frass arrangement ; lapponica and No. 1 would be linked 

 together with type 1, hetulicola and luteella with type 2, and distingu- 

 enda and continuella with type 3. But it will be more convenient, 

 perhaps, if they are rather grouped by their larvae, a plan which also 

 arranges them in pairs. Thus, the first pair (lapponica and No. I) are 

 characterized by mining with the back up, and showing distinctly the 

 cephalic ganglia ; the second pair (hetulicola and distinguendd) by 

 mining with the venter up, and showing the ventral cord ; and the 

 third pair (continuella and luteella) by mining with the back up, and 

 showing neither cephalic ganglia nor ventral cord. Under either ar- 

 rangement lapponica and No. 1 go together, so I will take them first. 



Lapponica and No. 1. The mines of both are long galleries of 

 moderate width, whose usual course is to follow a rib for some distance, 

 and then to turn off at a tangent till another is reached, which in its 

 turn is pursued ; but whether the ribs are taken as a guide or not, the 

 mine is never contorted, and this holds good even with their very 

 commencement, which, beginning in a delicate and hairlike manner, 

 stretches straight away at once from the site of the egg. So far, and 

 in a general view, the mines are precisely alike, but in the two portions 

 which answer to the first three skins of the larva, and which, from 

 their apparent insignificance, are apt to be overlooked, most excellent 

 and easily appreciable characters may be gathered. In the case of 

 laponnica it has already been pointed out, that the frass completely 

 fills these two portions of the mine, that it is coiled in the second of 

 them, and that its colour in both is green, thereby offering a striking 

 contrast to the third or main portion of the mine, in which the frass 

 is black, and collected into a narrow central thread. On the other 

 hand, the frass in No. 1 is black throughout, there is no coiling in the 

 middle portion, and a free margin borders its track in all three portions, 

 so that the character of the mine is uniform from beginning to end. 



