The male Eucera can be distinguished from those of _Anthophora_ and _Saropoda_, both by the differences in the number of the submarginal cells of the wing, and by the extreme length of its antennæ, whence the genus derives its name. In _Andrena_ and _Cilissa_, the males have usually lanceolate bodies. In the latter genus there will be no difficulty in associating the legitimate partners; but in _Andrena_, although general habit will usually bring the male within the boundary of the genus, nothing but experience, or specific description will associate the sexes correctly, there being in many cases an extraordinary discrepancy between them. These two genera themselves also can scarcely be distinguished apart, excepting by means of their trophi; _Cilissa_, however, in general habit greatly resembles the genus _Colletes_, especially the _Cilissa tricincta_, which might, upon a superficial glance, be almost mistaken for one of them. The male _Halicti_ have long cylindrical bodies and long antennæ, but from the male _Chelostoma_, which has a very similarly shaped body also and long antennæ, they may be distinguished by the differences in the number of the submarginal cells; and from those of _Sphecodes_, by the antennæ, which, in the latter are not relatively so long, and are usually moniliform. The thorax of these is also less pubescent, and the tinge of the red colour of their abdomen is different from that of the red male _Halicti_. The males of _Cœlioxys_ can be readily distinguished from those of _Megachile_, by the spinose apex of their abdomen. In _Megachile_, general habit will bring the males within the precincts of their genus, as well as their largely dilated anterior tarsi in some of the species. A difficulty similar to what is found in the distinction between _Andrena_ and _Cilissa_, arises in the separation of _Chelostoma_ from _Heriades_, and which we shall again meet with in drawing the line between _Anthophora_ and _Saropoda_. The difference can only be detected by examining the trophi, but a pin and a little patience will elucidate the separation. The males in all but two species of _Anthophora_ may be readily associated with their partners; but in these two the females are entirely black, and so hirsute as to have led Ray (wanting the knowledge of the use of the trophi and posterior shanks) to unite the one he knew with his _Bombylii_; their males are fulvous, and the latter have a remarkable elongation of the intermediate tarsi, from one of the joints of which also a tuft of hair or a loose lateral fringe projects, giving them thus a wider expansion, and the use of which is prehensile, the same as that for which the anterior tarsi in some of the _Megachiles_ and in our single _Anthidium_ receive their dilatation. This structure has also the effect of adding very considerably to the elegance of their appearance when they are in fine condition.