36 THE CLASSIFICATION OF BIRDS 



being prascoces ; but in spite of such important differences it has 

 been shown (Gadow, " Proc. Zool. Soc.," 1882, p. 312) that they 

 possess many points in common. The nostrils are impervious, 

 whilst those of the three other Orders of Charadriiformes are 

 pervious. The oil-gland is naked or wanting, whilst it is tufted 

 in the three other Orders. The vomer is vestigial or wanting, but 

 is well developed in the three other Orders. 



Of the five families associated together to form this group, the 

 Charadriidce and the Parridce are the only ones that possess basi- 

 pterygoid processes. The Parridce * differ from the Charadriidce 

 in having no . lateral occipital fontanelles. The Alcidce are 

 altrices ; the other four families are prsecoces. I know of no 

 difference between the Laridce and Cursoriidce except that the 

 former have webbed feet, a miserable character on which to found 

 a family. 



The Alcidce breed in the Arctic and Subarctic parts of the 

 Northern Hemisphere ; the Laridce and the Charadriidce are 

 almost cosmopolitan ; the Parridce are circumtropical ; whilst of 

 the Cursoriidce the Cursoriince are confined to the tropical parts 

 of the Old World, the Chionidince to Arctic South America, and 

 the Thinocorince to South America generally. 



13. GRUES. 



The almost cosmopolitan Cranes and the American Courlans 

 (Aramus) compose the Grues, and cannot be regarded as belong- 

 ing to different families. They are probably near relatives of the 

 Gavio-Limicolaa. Compared with the Charadriidce the Gruidce 

 have quite lost the opisthocoelous character of their dorsal verte- 

 bras, and all but lost their basipterygoid processes. 



14. PTEROCLES. 



The Sand-Grouse appear to form a connecting link between 

 the Limicolaa and the Columbag. They agree with both in having 

 basipterygoid processes. The Pterocles and the Limicolaa are 

 prgecoces, but the Columbae are altrices. The Pterocles and the 

 Colurnbse have the oil-gland nude (when present; it is occasionally 



* The statement (Gadow, " Bronn's Thier-Reichs," ii. p. 195) that Parra is 

 holorhinal is one of those curious accidents which requires the most careful 

 revision entirely to avoid. 



