128 MEMOIRS OF THE CARNEGIE MUSEUM 



From this it will be seen that both the proportionate and relative lengths of cer- 

 tain long bones of the limbs in these two species of birds slightly differ, but the dif- 

 ference is very slight. 



There is no especial association of characters in either the pectoral or pelvic 

 limbs of Phaethon that in any way remind us of the corresponding parts of the skel- 

 eton in a Gull, or a Tern, much less any kind of an Auk or a Puffin. The several 

 bones seem to possess a distinctive character quite their own. The humerus shows 

 a slight compression in the transverse direction, rendering its humeral head narrow, 

 and its very moderately curved shaft ellipsoidal rather than circular on section. 

 The well-marked ulnar tuberosity projects directly anconad, as does the prominent 

 radial crest project palmad, — the long transverse axis of the first being parallel to 

 the plane of the latter. At the proximal end of the bone, on its palmar aspect, just 

 before we come to the humeral head, we meet with a well-defined groove running 

 at right angles to the long axis of the shaft ; and this groove becomes very deeply 

 marked at a point on the opposite side of the bone from the ulnar tuberosity. 



The "pneumatic fossa" instead of being entirely open, as in a good many birds, 

 is covered across by a more or less perfect bony plate, which plate shows the single, cir- 

 cular pneumatic perforation at its center. This hole is smaller in proportion in my 

 specimen of P. flavirostris than it is in the other species. At the distal end of the 

 bone the fossa above the oblique and ulnar tubercles is fairly well scooped out ; 

 while on the ulnar side of the humerus at this end, both the pits for tendinal inser- 

 tion and the grooves for their passage are unusually well marked and deep. An 

 exceedingly rudimentary " epicondyloid process " can be seen, but it by no means is 

 the characteristic feature tha,t we find it to be in the humeri of the Laridss and 

 those suborders of birds most nearly related to them. 



The radius is straight and of a more or less uniform caliber, while its companion 

 bone of the antibrachium, the ulna, is considerably bowed, with its shaft presenting 

 three faces more or less distinctly. These might be here designated as a palmar face 

 or surface, an interosseous face, and a subanconal face. The line or angle formed by 

 the intersection of the subanconal and palmar faces, has along it the row of papillae 

 of the secondary quill-feathers ; and another indistinct row of them passes down 

 the middle of the subanconal surface. TJaere are fourteen such papillse in the first 

 mentioned row. The olecranon process is a very insignificant affair, while at the 

 distal extremity of the bone, at its anconal side, the end is drawn out into a dis- 

 tinct apophysis, which, in articulation, bends down towards the ulnare ossicle of the 

 wrist. Two segments compose the skeleton of the carpus in the adult, the usual 

 radiale and the just-mentioned ulnare. 



