bo PROCELLARIIFORMES 



horny sheath is separated by grooves into more or less distinct 

 plates, and the mandible may also be grooved, as in Phoehetria ; 

 while Prion is especially remarkable for the curious fringe of trans- 

 verse lamellae on the margins of the broad maxilla, which recall 

 those of the Duck tribe, traces of the same being exhibited by 

 Ossifraga, Fulmarus, Drqjtioyi, and Halolmena. The most striking- 

 peculiarity, however, is the tubular structure of the impervious nos- 

 trils, which trenchantly divides the Petrels from all other Birds ; 

 these tubes are far apart in the Diomedeinae, and lie laterally 

 towards the back of the culmen : in the remaining groups they 

 are fused together and are situated dorsally. In the Oceanitinae 

 the single aperture looks forwards and upwards, but in the 

 Procellariinae the septum is produced to the front, showing 

 clearly tlie double nature of the formation ; in Pdecanoules 

 again the distinct openings are almost vertical, an arrangement as 

 well adapted to the diving habits as are the long sternum and the 

 compressed wing-bones. The rows of retroverted spines found on 

 the palatal membrane in most of the family no doubt aid in the 

 retention of slippery prey, as do the lamellae in Prion. The 

 lower portion of the tibia is bare ; the metatarsus varies in 

 length and stoutness according to the species, though often 

 decidedly slender, and is much compressed in PuJfLnus and its 

 nearest allies. It is usually covered with hexagonal scales, but 

 Oceanites and Cymodromn show but one long anterior scute 

 ipcTca), while Garrodia and Pelagodroma have a series of 

 oblique plates instead. The hallux is absent in Pelecanoides, and 

 consists of only one phalanx elsewhere, being quite rudimentary in 

 the Diomedeinae ; it is slightly above the level of the anterior 

 toes, which are connected by large webs. The claws are, as a 

 rule, sharp, curved, and compressed, but are blunt and much 

 flattened in Pelagodroma, Pealca, and Cymodroma., showing a 

 similar tendency in others of the Oceanitinae. The wings are 

 normally long, and are very narrow and pointed in the Diome- 

 deinae, where the expanse is vast, Ijut in Pelecanoides they are 

 decidedly short : the primaries are eleven in number ; the 

 secondaries are ten or less in the Oceanitinae, thirteen or more 

 in the remaining forms, and amount to more than thirty in some 

 of the Diomedeinae. The tail is rarely long, as in Phoehetria, and 

 may be even, rounded, graduated, or emarginated; the above species, 

 Bidiveria, and some forms of Piifjinus have it wedge-shaped, while 



