1. _leucomelana_, Kirby, ♂♀. 3-4½ lines. (Plate XIV. fig. 3 ♂♀.) 2. _spinulosa_, Kirby, ♂♀. 3-4 lines. 3. _pilicornis_, Bainbridge, MS., ♂♀. 4-4½ lines. 4. _bicolor_, Schrank, ♂♀. 4-5 lines. (Plate XIV. fig. 1 ♂♀.) 5. _fulviventris_, Panzer, ♂♀. 4-5 lines. _Leaiana_, Kirby. 6. _ænea_, Linnæus, ♂♀. 3-4½ lines. _cærulescens_, Linnæus, ♀. _cærulescens_, Kirby, ♀. 7. _parietina_, Curtis, [V. 222.] ♂♀. 3-4 lines. 8. _xanthomelana_, Kirby, ♂♀. 4-7 lines. _atricapilla_, Curtis, [V. 222.] ♀. 9. _aurulenta_, Panzer, ♂♀. 4-6 lines. _tunensis_, Kirby. 10. _rufa_, Linnæus, ♂♀. 3-6 lines. _bicornis_, Linnæus. _bicornis_, Kirby. GENERAL OBSERVATIONS. Named from _ὀσμὴ_, _sweet-scent_, from some fancied idea of their possessing the property of emitting a sweet odour; but this, although it is the case with many of the bees,—for instance, with the genera _Prosopis_, _Halictus_, _Nomada_, some of the _Anthophoræ_, _Saropoda_, and the male _Bombi_ and _Apathi_,—I have not noticed in any of this subsection, the _Dasygasters_, and therefore not in any of the present genus. It is possible that when richly laden with pollen, this may emit some smell, but I am not aware that any of the scent of flowers lies in the anthers or their pollen, although this in some cases has a spermatic odour pointing to its express function; but be this as it may, such is their name. These as a group are what are called the ‘Mason Bees,’ from the habit they have of agglutinating particles of sand or earth mixed with minute pebbles, scarcely larger than grains of sand, or raspings of wood combined in the same manner, with a secretion which they emit, and of which they form their cells. The instinct of the creature prompts it to be speedy in the operation, as the material, like plaster of Paris, dries very rapidly to a hard substance. Whether they have the power of softening the edges as the manufacture of the cell proceeds is not known, nor whether, as they add the material, it instantaneously consolidates itself, but the colour of the structures themselves would indicate a simultaneous mixture. This could not be the case, if the mortar or mixture were formed away from the domicile and brought home in little pellets, each being added upon the insects’ arrival, although they obtain it all from the same spot, whence arises its uniformity in colour, and they are speedy in the formation of their nests. These cells are rather rough externally, according to the nature of the material of which they are composed, but they are very smooth within. The nature of the cells varies with the places of their deposit, which is dependent upon the idiosyncrasy of the species. Thus, those which construct their cells in wood, form them of moistened particles of wood, and those which make them in cavities of any kind, in the earth, beneath stones, or