572 STRUCTURAL CHARACTERS 



without aftershaft, and with thickened rhachis ; down feathers absent ; hallux on a level with 

 the front toes. 



1. FAMILY COLUMBIDJE PIGEONS. 



Ambiens present ; vestiges of caeca ; oil-gland vestigial ; no gall-bladder ; twelve rectrices. 



(a) Genus Columba. Tail shorter than the wing, truncated ; tarso-metatarsus partly 



feathered. (Vol. ii. p. 499.) 

 (6) Genus Ectopistes. Tail longer than the wing, narrow and pointed, the outer 



feathers broader than the centre ones. (Vol. iv. p. 506.) 

 (c) Genus Turtur. Beak slender, the membranous operculum covering the nostrils 



forming a tumid swelling ; tail much rounded. (Vol. ii. p. 505.) 



SUBORDER : PTEROCLES SANDGROUSE 



Nidifugous nestlings ; tarso-metatarsus extremely short, feathered ; hallux vestigial or 

 wanting ; cceca large ; vomer vestigial ; aftershaft vestigial ; tail of sixteen feathers. 



2. FAMILY PTEROCLHXffi. 



Characters as for the suborder. 



(a) Genus Pterocles. Hind-toe absent, outer primaries and middle tail feathers pro- 

 duced into filaments. (Vol. ii. p. 525.) 



SUBORDER: LARI 



Schizognathous, schizorhinal ; no basipterygoid processes ; vomer well developed ; large 

 supra-orbital grooves ; pervious nares ; feet webbed ; oil-gland tufted ; eleven primaries, outermost 

 vestigial ; wing diastataxic ; creca large ; ambiens present ; thoracic vertebrae opisthoccelous ; 

 eggs pyriform, double spotted. 



3. FAMILY ALCID^l AUKS. 



Young nidicolous, with abundant nestling down which is never spotted or striped ; sternum, 

 pelvis, and ribs all much elongated ; femur very short, causing a markedly vertical 

 carriage of the body ; tail very short ; sternum with a single pair of notches ; with an 

 apterion in the spinal tract. 



(a.) Genus Alca. Beak laterally compressed and grooved, the tomium of the upper 

 jaw markedly decurved ; nostrils lateral, slit-like, near the middle of the inferior 

 border of the jaw, and partly concealed by feathers ; tail pointed. (Vol. iii. p. 1.) 

 (6) Genus Uria,. Beak moderately long, laterally compressed, not dorso-ventrally 

 expanded, and without grooves ; nasal aperture partly concealed by feathers ; tail 

 short and rounded. (Vol. iii. p. 3.) 



(c) Genus Cepphus. Cannot be distinguished from that of Uria. (Vol. iii. p. 7.) 



(d) Genus Alle. Beak short, swollen, without grooves ; nostrils ovate, exposed. 



(Vol. iii. p. 9.) 



(e) Genus Fraterculus. Beak very large, brightly coloured, grooved ; height of the 



beak equal to its length ; with horny excrescence on eyelids ; legs and toes red ; 

 tail short. (Vol. iii. p. 10.) 



4. FAMILY LARIDJE GULLS. 



Young nidifugous, with mottled down, or of a uniform brown colour ; hinder border of 



