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Show 1899.] OSTEOLOGY OF THE TUBINARES. 403 between these and that of Diomedea seem sufficiently marked to entitle them to the rank of genera. The collection contains complete skeletons of two species of Diomedea. The hemipterygoid of the Petrel is here described and figured (Pl. XXIII. figs. 3, 4) for the first time. The indications of the Ciconiiform affinities of the Petrels pointed out by other writers have been verified and additional points brought to light. It would seem that the Petrels must be regarded as a very ancient group, undoubtedly by no means remotely allied to the Sphenisci, Colymbi, and the Ciconiiformes. Their Ciconiiform affinities are most clearly seen perhaps through the palate. That of Diomedea, for instance, presents many points in common both with Fregata and with Ciconia that can hardly be attributed to any other source than that of derivation from a common ancestor. The holorhinal nares, the temporal fossas, and deep supra-orbital grooves they share in common with the Penguins and the Divers. The pelvis of tbe Procellariidas seems to be traceable to a form most closely resembling that of the Penguins. That of the Diomedeidas is more specialized, and in the adult, at least, resembles not a little that of the Ciconiiform type. Besides the Petrels, the Grebes and Divers are the only other birds which have the cnemial crest greatly developed so as to rise high above the articular surface of the femur. This can hardly be regarded as an adaptation in the case of the Petrels, for they are not great swimmers, and do not therefore use their legs as do the Divers. As to the arrangement of the group in the present paper, I can only regret m y inability to adopt in toto that of any of those to whose works we are so greatly indebted; it is to be hoped that in the near future some sort of harmony will come of the existing somewhat unsatisfactory state of affairs. The present scheme-as adopted in this paper-though based largely on the osteologv, is not entirely founded thereon ; but has been framed with a due regard to the claims of other anatomical facts. xi. KEY TO THE OSTEOLOGY OF THE TUBINABES. A. SKULL. (Plates XXIL, XXIII.) The skull is holorhinal and schizognathous; with more or less deep supraorbital grooves; a large, laterally expanded vomer fused posteriorly with the palatines; an olfactory cavity of great size ; a large antorbital plate ; and a hooked upper jaw. A. Supra-orbital grooves without an external overhanging ledge; temporal fossae, when present, in the form of deep depressions approaching one another in the middle line, and tending to cut off the cerebral from the cerebellar portions of the skull; external nares large, divided into right and left apertures by a narrow bar of bone in the mid-dorsal line ; length of the upper jaw never greatly exceeding that of the cranium • orbito-sphenoid imperfectly ossified; basipterygoid processes well developed or in the form of minute prickles; with a conspicuous tubular parasphenoidal pneumatic aperture opening downwards above the Eustachian grooves; palatines long, sharply denned anteriorly at their junction with the maxillo-palatine processes, which are small and plate-like lamella? never projecting |