230 On the Grey Shrikes of Tunisia. 



certain^ there does not seem to be a gradual continuity of 

 intermediate forms connecting or uniting the two species ; 

 and secondly, that in the particular district where these non- 

 descript birds occur we do not find one constant type, but 

 individuals which vary in plumage among themselves, some 

 resembling more L. alc/eriensis, and some L. elegans, and 

 others again standing halfway between the two. 



On the other hand, in support of the alternative theory of 

 intermediate forms, may be adduced the argument that the 

 difference between the two Shrikes, L. algeriensis and 

 L. elegans, although sufficiently pronounced in typical 

 examples, is after all merely one of plumage-colouring, or, 

 to be more precise, I should say a difierence in the shade of 

 plumage-colouring and in the proportion of black and white 

 markings, this difference being subject to modification 

 according to the locality inhabited. Structurally there would 

 appear to be no difference whatever between the two 

 species. In the case of typically- plumaged birds, besides 

 the very marked difference in the shade of the general grey 

 colouring, both above and below, we have that of the marking 

 of the wings and tail-feathers, there being, roughly speaking, 

 more black and less white in L. algeriensis, and vice versa in 

 L. elegans, and these points of difference seem to be fairly 

 constant, so long as we confine ourselves to typical speci- 

 mens. When, however, we leave these, we find the difference 

 between the two species less marked and no longer constant; 

 and when we come to birds like those occurring in the 

 particular Central Tunisian district I have mentioned, it is 

 absolutely impossible to decide to which of the two species 

 they may belong. 



At the same time 1 feel bound to confess that, until I met 

 with these intermediate birds last spring, I never experienced 

 any difficulty in referring specimens obtained to either one 

 or the other of the two species. 



The presence or absence of the white superciliary streak 

 is not a distinguishing feature, as, although but faintly 

 indicated, it is generally to be observed in specimens of 

 L. algeriensis as well as in L. elegans. 



