This interesting and peculiar parasite was apparently first noted and studied by George Newport in 1831. That writer, however, was unable to publish his observations till 1849, by which date he had been anticipated in authorship by Francis Walker for the specific name, and by J. O. Westwood for the generic. With the latter Newport engaged in a somewhat protracted controversy touching priority of name, morphology, habits, etc., of Melittobia. There can be no doubt that Westwood's genus, very briefly characterised in Proc. Ent. Soc. Lond. for 5th July, 1847, p. xviii, must stand. The part of the proceedings containing this page was published on 12th January, 1848. As the purpose of the present notes is chiefly to offer a more accurate description of M. acasta, and as, besides, I am at present engaged in revising the whole genus, it does not seem necessary to say much on the habits of the insect. M. acasta is markedly polyphagous; never apparently a true hyperparasite, it attacks everything within its limited range of action. Already it has been bred from a long list of hosts, and somewhat contradictory conclusions about the insect's parasitic status and economic value may be drawn from its host attachment. Thus it may be a pest in nests of bees, wasps, etc.; a species of Melittobia again proved a serious menace in the laboratory to Tachinids introduced into the U.S.A. to combat the Gipsy Moth, but possibly, the insect plays, or may be induced to play, a useful part in destroying dipterous puparia in or near houses, or in surroundings where the adult may skulk secure. For Melittobia dislikes light, and the ♀ flies little, though when once established in a suitable environment, it is hard to dislodge.