1867.1 PROF. HUXLEY ON THE CLASSIFICATION OF BIRDS. 455 



the Plovers and their alhes as the most central group of tliese birds, 

 we may pass, without a break of more than family importance, along 

 several distinct series, or gradations, of ornithic forms. 



Thus, along one line, the Bustards are intermediate between the 

 Plovers and the Cranes ; while Psophia and Rhinochefus lead from 

 the Cranes to the Rails. 



Following another line, Hemipodius stands between the Plovers 

 and the Fowls ; while Si/7rhaptes inclines, on the one hand, to the 

 typical Gallinaceous birds, and on the other to the Columhidce. 



A third series is commenced by the Gulls. The osteological re- 

 semblances between a Plover, a Gull, an Auk, and a Diver are so 

 close that it is utterly out of the question to regard these Birds as 

 members of different orders. But the Gulls grade insensibly into 

 the Procellariidcje ; and, though the Apterodytidce appear to be sepa- 

 rated by a broad gap from the Alcidce, Alca impennis, in the form 

 of its humerus, in the mode of articulation of the radius and ulna 

 with the humerus, in the proportions and structure of the tarso- 

 metatarsal bone, shows itself to be an almost intermediate form. 



I am acquainted with only two birds, Dicholophus and Crax glo- 

 bicera, the structure of the skull of which would lead me to regard 

 them as transitional between the Schizognathous and the Desmo- 

 gnathous sections, or, at any rate, as approaching the latter division. 



Nitzsch and Burmeister have assigned to Bicholoj)hus a position 

 near the Cranes and the Rails, and, no doubt, justly on the whole, 

 though I venture to think that they have underrated the points of 

 resemblance to the birds of prey, and especially to Gypogerunus. 

 In the skull of Dicholophus the internasal septum is ossified to a 

 very slight extent, and the maxillo-palatine processes may meet in 

 the middle line, in both of which respects it approaches the birds of 

 prey. But the ossified part of the nasal septum does not unite 

 below with the maxillo-palatines ; and in this respect Dicholophus is 

 unlike the Raptorial birds*. 



Crax (jhhicera, on the other hand, while it retains the charac- 

 teristically Gallinaceous basipterygoid articular surfaces, palatine 

 bones, angle of the mandible, and other peculiarities, has a jiartially 

 ossified nasal septum, which divides below and unites with the 

 maxillo-palatines, just as in the Raptorial birds. 



The Cucididce and Alcedinidce occupy nearly the same middle place 

 in the Desmognathous series that the Plovers have among the Schi- 

 zognathous families. The MusophayidcR bring them into relation 

 with the Raptorial birds, the Rhamphastida. with the Parrots, the 

 Podargidce with Cancroinaf, and so with the Herons and Storks. 

 But these last are clearly afltined, on the one hand, with the Cor- 

 morants and Pelicans, on the other with the Flamingos, and through 

 the latter with the Laraellirostres. 



* Mr. Parker is inclined to lay a still greater stress than I have done upon the 

 many Raptorial characters of Dicholophus. 



t A hazardous suggestion, hut one the temerity of which will perhaps apjiear 

 less after a careful comparison of the skulls of these two hirds. 



