Pollen conveyed on the venter. Two submarginal cells to the wings of all. Abdomen subclavate. First three joints of labial palpi continuous, terminal joint inserted before apex of third - =CHELOSTOMA (21).= First two joints of labial palpi continuous, two last inserted before the apex of the second - =HERIADES (22).= Abdomen obovate, rounded at apex - =OSMIA (24).= Abdomen truncated at base. Segments slightly constricted, and not spotted with colour - =MEGACHILE (19).= Segments not constricted, spotted with yellow - =ANTHIDIUM (20).= Pollen conveyed on the posterior legs. Two submarginal cells to the wings. Abdomen lanceolate; antennæ clavate; posterior legs covered with long hair - =PANURGUS (9).= Abdomen obovate; antennæ filiform; posterior legs covered densely with short hair - =EUCERA (10).= Three submarginal cells to the wings. Short dense hair on the whole posterior tibiæ externally. Abdomen obovate; first joint of labial palpi twice as long as second - =ANTHOPHORA (11).= Abdomen subrotund; first joint of labial palpi six times as long as the rest - =SAROPODA (12).= Long hair, but loose, on the entire posterior tibiæ, externally and internally. Abdomen subclavate - =CERATINA (13)= Curved hair fringing the edge only of the posterior tibiæ, the centre glabrous. Body densely hirsute, spurs to all the tibiæ - =BOMBUS (26).= Body subpubescent, no spurs to the posterior tibiæ - =APIS (27).= -------------- It will be desirable to add a few observations to the preceding table to facilitate its use, and because, as many of the characters upon which it is framed are exclusively those of the female, it is necessary to point out the differences of their males, that the sexes of the genera may be duly recognized and associated. It may be first noticed generally that the antennæ, in the males, are not usually geniculated at the scape, which is nearly always the case in the opposite sex, and they are also, with rare exceptions, always longer than those of their females. In _Colletes_, _Prosopis_, _Dasypoda_, _Panurgus_, _Ceratina_, _Nomada_, _Melecta_, _Epeolus_, _Stelis_, and _Anthidium_, the habit or colouring of the males is so similar to that of the females, that their genus may be thus at once determined, and, in fact, the brief characters in the table will embrace them.