MONOGRAPH OF THE PETRELS. 



is absolutely no growth pause, the rami of the one passing directly, insensibly, into 

 those of the other and, so far as I know, this peculiarity is met with only 

 among the Petrels and has not hitherto been described. 

 Pterylologically the Petrels approach the Ciconiiformes. 



OSTEOLOGICAL ChABACTEES. 



Osteologically the Petrels can readily be divided into two families — Procellariidce 

 and Diomedeidce ; and this, whether the evidence is taken from the skull, the 

 trunk, or the limbs. The nature of this evidence is set forth in detail in my paper 

 in the Proceedings of the Zoological Society for 1899. 



The Procellariidce must, it seems to me, be divided into two sub-families — 

 Procellariince and Pelecanoidince. The members of the last stand well apart from 

 those of the first named, differing conspicuously in the characters of the skull. 

 Other well-marked differences, such as the relatively great elongation of the 

 sternum, the flattening of the wing-bones ; and the elongation of the ribs and 

 pelvis are to be set down to adaptation, and are therefore of no importance 

 from a systematic point of view. But in the great width of the basi-temporal 

 platform, and the prominent basipterygoid processes, the Pelecanoidince stand alone, 

 recalling the Penguins in these particulars and in the form of the pterygoids. 



Macronectes is undoubtedly the most highly specialized of the Procellariince and 

 herewith must be associated Fulmarus, Priocella, Thallassoeca, Pagodroma and Daption, 

 an arrangement first propounded by Forbes. Prion, in many respects resembles 

 Daption, but in its pelvis recalls Bulweria and (Estrelata. 



Procellaria, Halocyptena, and Oceanodroma on the one hand, and Fregetta 

 Pelagodroma, Gymodroma, Oceanites, and Garrodia on the other hand, seem to 

 represent two well-marked groups standing somewhat apart from the rest of the 

 Procellariince, but not sufficiently distinct to deserve the rank of a sub-family ; and 

 certainly not family rank, as was accorded by Forbes. 



The Diomedeidce have undergone specialization in many ways, in regard to 

 the skeleton as in other characters. The palate shows this specialization very 

 markedly, for though schizognathous, it approaches very near to becoming 

 desmognathous. Basipterygoid processes are absent. 



The thoracic vertebrae bear no hypapophyses. The corpus sterni is conspicuously 

 pneumatic ; and the carina merges into the sternal plate some distance cephalad of the 

 metasternum, while the posterior lateral processes project far beyond the level 

 of the metasternum. The humerus is pneumatic, and the crista inferior is inflated 

 along its preaxial border. The hypotarsus is simple, and the fibular ridge feebly 

 developed. 



xvm 



