Art. XXIV.—On the Species forming the Genus Ocydromus, a peculiar Group of brevi-pennate Rails. By Walter L. Buller, C.M.G., Sc.D., F.L.S. [Read before the Wellington Philosophical Society, 12th January, 1878.] Although as a group the limits of the genus Ocydromus are sufficiently well defined, considerable difficulty has been experienced in determining the species. Every naturalist who has studied the subject appears to have arrived at some different conclusion as to the number of constant forms; and where the variances as to size and plumage are so well maintained it is difficult to avoid drawing specific distinctions. If, however, it can be shown that all these extreme forms graduate in a series, or, in other words, run into one another, it becomes impossible to find any fixed aberrant characters. Without professing to be able yet to place the matter beyond all dispute, I venture to think that the series of specimens which I have the honour to exhibit this evening affords pretty strong evidence that several of the so-called species in the South Island must be united under the name of Ocydromus australis. In my “Birds of New Zealand,” I admitted only three well-ascertained species as inhabiting New Zealand—namely, O. earli, O. australis, and O. fuscus. I mentioned in the introduction to that work that, although Dr. Finsch recognized a fourth (O. troglodytes, Gmel.), I was unable to draw any specific line. Nevertheless, I pointed out very fully, in my account of the South Island wood-hen, the great variation both as to size and markings which that species exhibits, especially among birds from different localities. Captain Hutton, in an article on the New Zealand Wood-hens, read before this Society* “Trans. N.Z. Inst.,” VII., p. 110. in September, 1873, agreed with Dr. Finsch in admitting O. troglodytes, and added two more species of his own under the names of O. hectori and O. finschi. He further described a “variety or immature” example of this last-named species, which he suggests may “possibly be identical with Gallirallus brachypterus, Lafr.” Dr. Finsch, in a paper† “Trans. N.Z. Inst.,” VII., p. 226. written the year following, professes to identify Ocydromus troglodytes with the O. australis of my text, page 170, but not the plate; of O. hectori he remarks, “I consider this a good species after having compared a typical specimen;” and of O. finschi he says that, having examined the type, he considers it a good species, although not without some suspicion that it may prove to be a variety of O. fuscus. He confuses Ocydromus australis, Sparrm., with the well-known O. earli; and with respect to the latter in Hutton's list, he makes the following singular statement:—“Dr. Buller, in his great work, unfortunately does not mention