298 BRITISH BEES. 



place them end to end, but where it is more roomy they 

 affix them side to side, completely adapting themselves 

 to the circumstances of the locality as I shall instance 

 below, in the description of the special habits of the 

 more conspicuous species. I have elsewhere referred to 

 the metallic colouring of many of the species of this 

 genus, and amongst them is found the greatest sexual 

 disparity of personal appearance, the 0. leucomelana, 

 and one or two of the neighbouring species being, per- 

 haps, the only ones wherein uniformity of appearance 

 would unite the partners together. The majority are 

 very pubescent insects, and the females of the terminal 

 species in the foregoing list are remarkable for a couple 

 of inwardly curved horns, springing from the base of the 

 clypeus just below the insertion of the antennae, an ap- 

 pendage usually a male attribute. 



There is very great dissimilarity in the habits of the 

 various species, whence no single characteristic will em- 

 brace them, nor is there any distinctive feature whereby 

 the genus might bear subdivision, either from habits or 

 habit, as will be collected from the following cursory 

 survey of their special natural history. 



Thus the first species, the 0. leucomelana, named so 

 from the white decumbent down which edges the black 

 segments of the abdomen, extracts the pith from bram- 

 ble-sticks, and its cells are formed and closed with a 

 composition made of triturated wood or leaves. The 

 cylinders it forms are usually about five inches deep, 

 and within this it constructs about the same number of 

 cells proportionate to the small size of the insect. These 

 are midsummer insects, coming forth in June and July ; 

 they are very local, but seem to abound in the vicinity 



Bristol; whence Mr. Thwaites formerly sent me speci- 



