SUMMARY.The group of birds which we collectively designate the “Ratitæ” is the same as that to which this name was originally given by Merrem in 1813 (with the addition ofApteryx, then unknown), on account of the fact that all agreed in the absence of a keel to the sternum. They were “raft‐breasted,” in contradistinction to the Carinatæ, or keel‐breasted1Nitzsch, Huxley, Newton, Sclater, and Sharpe have successively adopted Merrem's subdivision of the class Aves–adding the Saururæ, unknown to Merrem.Other workers, both before and since Merrem, have accorded to the “Ratitæ” no greater prominence than that of an order or suborder of the class Aves. Sometimes even this was considered too great a distinction, and they were reduced to the rank of a Family, including such forms as Bustards, Plovers,&c.The “Ratitæ” of Merrem were apparently regarded by that author, as well as by Huxley, Newton, Sclater, Sharpe, and other systematists, as a monophyletic group. Fürbringer, Gadow, and Parker stand prominently forward as advocates for a polyphyletic origin.Gadow's views are admirably set forth in his contribution to Bronn's ‘Thier‐Reich’ [26]. Briefly, he regards the “Ratitæ” as a morphologically monophyletic group, standing in the same relation to the class Aves as the Anthropomorphæ to the rest of the Mammalia.With this view we entirely agree. We venture further, and include theCrypturiwithin the group. This was done long since by Garrod [30] and Stejneger. Beddard [7], later, has shown a strong inclination to follow suit. Thus, he says:‐ “It is unquestionably to theStruthionesthat they showed the greatest number of important likenesses, so much so, indeed, that their inclusion in one great group with them would be by no means an unreasonable way of disposing of them.”The Dromæognathous palate is sufficent justification for such an association. Consent to this, however, renders inoperative the old term “Ratitæ,” which at best is but a makeshift; for many of the Carinatæ are Ratite, whilst the Tinamous have a large keel to the sternum.We propose instead the termsPalœognathœ(Ratitæ+ Crypturi) andNeognathœ(Carinatæ–Crypturi). The adoption of these surmounts the difficulty indicated above.Gadow regards the Struthiones as a group of primitive forms more nearly representing Proto‐Carinatæ than any other living birds. Their retention under the common name “Ratitæ” he regarded as convenient rather than an indication of close affinity.Similarly we regard thePalœognathœas the unsuccessful descendants of protocarinate forms, but retaining probably but few of their characteristics unaltered. It would be too much to regard any of the existingNeognathœas the direct descendants of any of the existing or extinctPalœognathœknown to us, but it seems not improbable that their source may be traced to that stock which gave rise to the Rheo‐Dinornithine type of palate and pelvis.Casuarius, which forms the nucleus of this research, is here regarded as only generically distinct fromDromœus. These two forms are, it is here contended, closely allied.Struthiois perhaps derived from the same ancestral stock. Hitherto, however, these two forms,CasuariusandDromœus, have been regarded as more closely allied toDinornisandApteryxthan any other forms.Apteryxwe regard as quite distinct. The interrelationships of this group are indicated in the diagram (p. 265).The skeleton ofDromœus ater, procured at the last moment, at great trouble, by Mr. Rothschild, has proved of considerable interest in one or two respects. It does not differ much, however, from that of the larger species: wherein it differs it appears to approach the Cassowaries. I have seen no authenticated skeleton ofD. irroratus.Skulls of adultCasuariusandDromœusare badly needed; as also is the adult skeleton ofRhea darwini. It is interesting to note that the characteristic feathered tarso‐metatarsus ofR. darwiniis temporarily reproduced in the embryo ofR. americana(fig. 2 D, p. 155).Whether the four species of Ostrich indicated in this paper will be further confirmed is a point which time alone will show. It seems probable.I hope to be able to supply much that is lacking in this paper by a further contribution at no distant date in the shape of an Appendix. Since this was written the British Museum has acquired a hind‐limb ofGenyornis. This is remarkable chiefly on account of the fact that digit II. was becoming absorbed. The proximal phalanx was of great length and slenderness. In this we may trace the early stage in the evolution of a second two‐toed Struthious bird. As