In a collection of bird-remains sent to Dean Buckland from North Island, New Zealand, in 1842, Professor Owen noticed a tibia which he regarded as belonging to a very small species of Dinornis, to which he gave the name Dinornis otidiformis. A few years afterwards further material showed that this bird was not Dinornithine at all, but was probably a gigantic flightless rail, and it was therefore referred to a new genus, Aptornis. Subsequently, on the evidence of a nearly perfect skull, considerably larger than that of A. otidiformis, a second species, A. defossor, was described, and it is to this larger form that the fine skeleton figured on Plate X belongs. The bones from which this specimen was reconstructed were found in 1889, by Mr. W. S. Mitchell, in a chasm in the Limestone at Castle Rocks. Southland, New Zealand; together with them occurred more or less complete skeletons of Harpagornis (both species), Notornis, a large species of Fulica, allied to that recently discovered by Dr. H. O. Forbes in the Chatham Islands, a small Ocydromus, Stringops, Anas, Apteryx, and also Anomalopteryx didina and A. didiformis. A very interesting account of the mode of occurrence of these remains has been given by Mr. A. Hamilton, to whose papers those interested may be referred for further information on this point. The same writer has also given a brief description, with numerous measurements, of the bones of the species with which we are now concerned. It appears that the more or less perfect skeletons of several individuals were found mingled with one another; and, although the greater number of the bones constituting the present specimen no doubt belonged to a single bird, the missing ones have been replaced by portions of the other skeletons.