May, 1894.] 97 



Continuella and luteelln. There is just as little similarity in the 

 mines of these two species as in those of the preceding pair, and had 

 the grouping been based upon this ground instead of upon the larvae, 

 continuella must have gone with disfinguenda, and luteella with betuli- 

 cola. My remarks will, therefore, have to be directed to this cross 

 resemblance. Like distinguenda, continuella is a very perfect example 

 of the mine with a small transverse capacity and coiled f rass, the want 

 of capacity in the former depending on the extreme narrowness of the 

 mine, and in the latter upon the very partial manner in which the 

 parenchyma is removed. They can, however, be readily distinguished 

 from one another. Continuella is a much larger mine, it is filled with 

 greenish frass, and begins invariably from a brown bunch of convolu- 

 tions of some size, placed in an angle of the midrib ; whereas, the 

 other starts from a point, without any series of twists and turns or 

 sign of discolouration, and contains brown frass. To distinguish be- 

 tween the mines of luteella and hetulicola is a much harder matter. 

 The relative breadth of the frass-track (about half filling the mine in 

 hetulicola , 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 be rash sometimes 

 to say to which of them a mine belonged. There are other small 

 points of difference, but I need not particularize 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 betulicola, luteella also 

 occasionally mimics the mine of distinguenda by a rough attempt at 

 coiling, but so clumsy is the counterfeit that it ought never to deceive 

 the collector. 



Utterly unlike in their mines, in their larvse continuella and 

 luteella are closely related. Both larvae are yellow, with pale brown 

 heads, and no trace of either cephalic ganglia or ventral cord. Luteella 

 may be known out of the mine by the urinary tubes, but they are not 

 dark enough to be seen when the creature is in the mine. Continuella, 

 yellow though it be, looks in situ green, and a very decided green too, 

 in consequence of the light reflected from the floor of its mine. Both 

 species are double brooded. Continuella almost restricts itself to the 

 downy variety of the birch, selecting the leaves at the ends of the 

 uppermost shoots ; and its cocoon varies from dark brown or blackish- 

 brown to olive. The cocoon of luteella is white or pale buff. 



