52 [March, 



any positive proof that even the most dissimilar among these forms 

 may not be mere varieties of one and the same species : for, after all, 

 certain forms, which we are practically sure are only varieties of 

 litferata, differ quite as much from one another in coloration — and 

 differ in the same directions — as nassata $ differs from thornleyi ? or 

 coqueberti ? . Neither, however, have we any positive proof of the 

 contrary : for it is perfectly conceivable that, in one species of a 

 genus, coloration may vary indefinitely, and in another be normally, or 

 even invariably, constant. We may suspect, but we cannot be sure, 

 that the coloration of any particular form is (or is not) constant, till 

 we have watched it through successive generations, or found that it is, 

 or is not, correlated with a habit of pairing only, or at least normally, 

 with some particular form of the opposite sex. In this case no such 

 observations are yet on record. 



(2) Now as to the "pictura albida vel flava." This is a veiy 

 beautiful and conspicuous ornamentation of certain particular 

 divisions only of the integument, with brilliant white or yellow (cpiite 

 distinct from the duller yellows of the ground-colour), which appears 

 in every British Tenthredopsis form without exception, but is much 

 more developed (i.e., more extensive) in some forms than in others. 

 At the very least it occupies the mouth parts (labrum, etc.) with more 

 or less (usually the whole) of the clypeus and the scutelhim (perhaps 

 also the cenchri— at any rate, for whatever reason, these are white or 

 whitish in all our species ! ) . In its extreme developments it extends 

 very much further, i.e., to some or all of the following parts : — 

 almost the whole head (gense, tempora, and orbits of eyes ; the apices 

 of the supra-antennal tubercles occasionally), also the edges of the 

 pronotum with the tegulse ; the posterior corner (rarely) of the " middle 

 lobes " of the mesonotum ; a triangular appendage at the apex of the 

 scutellum, the post scut ellum and certain sclerites following it ; the 

 pleura?, sterna, coxa3, and trochanters, and finally the apical margin of 

 the propodeum. Further than this point, in the posterior direction, it 

 never goes; so that we may say, "pictura albida in a Tenthredopsis 

 ends exactly where rufescence begins ! " 



(To be continued). 



