The _M. Willughbiella_ and _maritima_ prefer decaying wood, and they have been found upon decaying Willows in the Midland Counties in extreme abundance; they might be called gregarious were the material within which they burrow connected in a continuous plane. The _M. Willughbiella_ makes use of the leaves of the Rose and of the Laburnum, but the _M. maritima_ seems to prefer the leaves of the Sallow. The _M. circumcincta_ invariably burrows in banks, confirming the semi-gregarious habits of the genus, where it forms large colonies, and it is only by accident that it constructs secluded and solitary nests; it also makes use of rose leaves for lining its apartments. The insects are subject to the molestation of bee-parasites of the genus _Cœlioxys_, the _C. quadridentata_ having been bred from the cells of this latter species,—that parasite also frequenting the _M. Willughbiella_, and the _C. vectis_ is well known to infest the _M. maritima_. Thus, it appears to be only the species of this division with the dilated tarsi that are exposed to such incursions, there being no record of parasites frequenting the division in which the males have simple anterior tarsi. Besides this bee-parasite, they are also subject to the attacks of some dipterous insect, whose larvæ destroy the larvæ of the _Megachile_. Much difficulty exists in separating the females of some of the species from each other; in others the specific character is sufficiently noticeable. It is a singular concomitant that those males with the dilated anterior tarsi have the apical joint of the flagellum of the antennæ considerably compressed and also dilated laterally. The proceedings of these bees are very curious. Although the tubes they usually form are long, they are so constructed as not to branch far away from the exterior of the material into which they bore,—sound or putrescent wood or earth, or old mortar joining the bricks of walls,—if in the second material, they usually follow the putrescent vein, and their tunnel in every case is rarely further than an inch or an inch and a half from the external surface. Both the sides of the tube, and the cells they form within them, will necessarily vary in diameter and length with the size of the species, but in the larger species they are about an inch and a quarter long and half an inch in diameter. Some entomologists have surmised that different species use the leaves of different plants for lining their cells; this, however, is not strictly the case, as shown in the preceding remarks; but, although not so, the series of nests in the same tube are always lined with cuttings from the same plant; perhaps a varying caprice operates upon each day’s labours and changes the plant, influenced by the drift of the wind or some casual freak.