3S4 HYMENOPTERA ACULEATA. 



comfort of the community. From the observations of 

 different writers it would appear that the various species 

 do not always keep to the same host ; carefully noted 

 observations on this point are, however, much wanted. 

 The following associations, I think, are probably right: 

 P. rupestris with B. lapidarius j P. vestalis with B. ter- 

 restris ; P. Barhutellus with B. hortorum ; P. qiiadricolor 

 (Barhutellus, Sm.) with B. pratormn and Jonellus ; P. 

 carnpesfris (according to most authorities) with £. mus- 

 corum and venustus, but according to Smith with hortorum 

 and Latreillellus. 



Pdthyrus resembles Bomhus in habits of life ; the females 

 pass the winter in an impregnated state, and lay their eggs 

 in the spring in the cells of the Bomhus. Mr. F. W. L. 

 Sladen informs me that the ? Psithyrus on entering the 

 nest of a Bomhus, at least in the cases of B. terrestris and 

 lapidarius, fights the ? belonging to the nest and kills her, 

 and then makes little waxen cells for her own eggs on some 

 prominent portion of the comb ; the first hatched out are 

 males, and both sexes leave the nest as soon as they are 

 fully matured. Structurally the genus is almost identical 

 with Bomhus, but the posterior tibiaa are devoid of any 

 polliniferous arrangement of hairs. Labial palpi four- 

 jointed, maxillary palpi two-jointed ; wings usually darker 

 than in Bomhus, with three submarginal cells ; abdomen as 

 a rule less densely hairy, and in the $ incurved at the apex, 

 the apical ventral segment more or less callose on its 

 posterior margin ; posterior tibiae in both sexes convex, 

 dull, and hairy, the posterior metatai'si in the ? without a 

 basal spine on the outer margin ; in this respect the ? differs 

 very widely from that of Bomhus, but in the ^ the diffe- 

 rence is less marked ; still, in this sex, the face oi Psithyrus is 

 always much shorter and rounder, and the external margin 

 of the tibia is always fringed with short hairs, whereas in 

 Bomhus the hairs of the fringe are very long ; the surface of 

 the tibife also is always duller in Psithyrus. The distribution 



