( cxcvii ) 



white or yellow, while that of the $ is either entirely black 

 (Andrena usually, Eucera and Anthophora sometimes), or with 

 the white or yellow much diminished and sometimes [Prosopis 

 usually, Anthidiiom sometimes) reduced to mere spots. Again 

 in many Wasps a completely yellow clypeus is a (^ character. 

 The sexes of Fossors differ less in this respect ; but even there 

 on the whole the (^ ,^ have the face more brightly coloured. 



Again the scape or basal joint of the antenna is often white 

 or yellow in front in ,^ (^, while it is black in their 5 $. The 

 whole under- (or front-) side of the ^ antenna is often paler 

 than that of the 5. And very conspicuous white or yellow 

 front-tarsi (sometimes also front-tibiae) is sometimes a male 

 character both in Fossors and Bees {e.f/. in several species of 

 Crahro and Megachile). 



The difference of colour in the $ and $ face is particularly 

 remarkable in the Bee-genera Andrena and Frosopis. British 

 Andrena spp. most commonly have their faces black or at 

 least fuscous in both sexes. But some of our own species, 

 and a very large number of those occurring round the Mediter- 

 ranean, have the clypeus or even the whole face white or 

 yellow ; and these colours (except in stylopised specimens) 

 hardly ever occur in their ? ?.* Again, in Prosopis the $ face 

 is almost invariably white, while that of the $ shows at most 

 a pair of small spots or streaks between the clypeus and the 

 eyes. In just one species {cornuta) both sexes have the face 

 entirely black ; but here the $ only has an enormously dilated 

 yellow " scape," which produces quite an equivalent for the 

 usual sexual contrast. In Halictus nearly all males exhibit 

 pictura albida on the clypeus, but only at its apex : while the 

 9 clypeus is, I believe, invariably immaculate. 



Though " pictura albida " on the front of the body is usually 

 a $ sexual character, on the abdomen it generally occurs, if at 

 all, equally (or nearly so) in both sexes, though there are 

 exceptions to this (the $ only exhibiting it) both among the 

 Fossors (as Myzine) and the Bees (as some spp. of Nomada). 

 In the latter situation, I believe it is generally a Protective 

 character (Synaposematic) ; but in the former, I suspect that, 



* I have only seen two Andrena spp. (one from Greece, and one from 

 Palestine) with any white or yellow on the face of the unstylopised ?. 



