382 ME. w. p. PTCEAFT ON THE [Mar. 21, 



Tubinares in the very valuable memoirs of Milne-Edwards (14), 

 Brandt (3), Huxley (12), Forbes (5-6), Gadow (8-9), Lydekker 

 (13), aud others. Nevertheless, in working carefully through 

 the collection of skeletons of this group in the Bi'itish Museum, 

 I found that much yet remained to be done, in the way of bringing 

 these facts together, so that, cai'efully sorted, they might be brought 

 yet more fully to bear upon the question of the systematic position 

 of the group. In this I think I have had a fair measure of success. 

 Besides also I have been enabled to add, here and there, a few 

 original observations. 



Following the plan of my last paper, I propose first of all to 

 deal with (ii.) the Adult Skull, then with that of (iii.) the Nestling, 

 following this with (iv., v.) the Axial Skeleton, (vi.) the Sternum 

 and Pectoral Girdle, (vii.) the Pelvic Girdle, (viii.) the Pectoral 

 Limb, and (ix.) the Pelvic Limb. 



ii. The Skull of the Adult. 



The skull of the Petrels, like that of the Impennes and Colymbi, 

 is schizognathous, holorhinal, and marked by deep supraorbital 

 grooves ; but it can at once be distinguished therefrom by its large, 

 laterally expanded vomer fused posteriorly with the palatines, an 

 olfactory cavity of great size — except in Pelecanoides and Pnffi,nus 

 assimilis,— and the markedly hooked upper jaw. The mandible 

 retains a distinct dentary suture and coronoid, the free end of 

 which last terminates in a more or less heai't-shaped expansion. 

 The angulare is truncated, and the internal angular process is small. 



The Occipital Region. — The dorsal border of the supra-occipital 

 region in the Procellariidee is strongly arched ; in the Diomedeidae 

 the curve of this border is very slight. The curve is produced 

 downwards on either side into the paroccipital processes, which 

 project, or rather depend, from the skull in the form of conical 

 " bosses." The aperture of the foramen magnum varies in form 

 and size. The occipital condyle is sessile, save in Diomedea exulans, 

 in which it is produced backwards on a stout base so as to 

 project considerably behind the foramen. In certain genera — 

 e. g., Thalassceca, Dajjtion, (Estrelata, Prion, PrioceUci, some species of 

 Pirffinus, Oceanites, Ci/modroma, Pelagodroma, and Procellaria — the 

 supra-occipital presents the concavo-convex form so characteristic 

 of the Sphenisci. In other forms this swelling is hardly 

 perceptible. 



The Roof of the Cranium. — The fron to-parietal region is more 

 or less furrowed in the median line, thus indicating the position 

 of the pallial cerebral fissure ; similarly, in many cases — TliaJas- 

 sceca, Priofinus, CEntrtlata, Pvffinus — the cerebellar prominence 

 is transversely ridged, the ridges corresponding to the under- 

 lying sulci of the cerebellum. The temporal fossae vary much 

 in the extent of their development. In Priofinus, Fulmarus, 

 Majaqueus, Ossifraga, and many species of (Estrelata and Pufflmcs 

 they rise dorsally so as to be divided only by a narrow median 



