COLUMB^ 155 



with great facility for a long time and for a very considerable 

 distance. 



The example obtained by Ayres was shot in a lagoon alongside 

 the Vaal Eiver ; it was constantly diving and did not attempt to fly ; 

 the stomach contained water snails. 



Nothing is known of its eggs or nidification but I suspect that 

 the eggs ascribed by Butler to the White-backed Duck were really 

 those of this species, as they agree very closely with those of other 

 members of the genus Erismatura. 



Order X. COLUMB^ffi. 



The Pigeons form a well marked group, with no clearly well- 

 defined relationships, except perhaps to the Sandgrouse (Pterocletes). 



They are birds of moderate size, with short legs and toes without 

 a trace of a web ; the bill is very characteristic, the distal portion 

 being slightly swollen and hard, and the proximal portion, in which 

 the nostrils open, covered by a soft skin, forming what is called the 

 , cere ; there are eleven primaries ; the number of tail feathers varies 

 from twelve to twenty ; the hallux, which is always present, is 

 jointed on a level with the other toes. 



The young, when hatched, are naked and helpless, and are 

 entirely dependent on their parents for a considerable time. 



Anatomical characters are : — Skull schizognathous and schizo- 

 rhinal ; basipterygoid processes present ; angle of the mandible not 

 produced behind its articulation with the quadrate ; no aftershaft 

 to the feathers ; a well developed crop ; oil gland, if present, naked ; 

 deep plantar tendons galhne (see Vol. III., p. 2, fig. 2b) ; caeca 

 rudimentary when present ; two carotids ; ambiens muscle present 

 or absent, the other four Garrodian muscles almost always present. 



The distinctions between the families and subfamilies of this 

 Order, as usually recognised, are not of very fundamental impor- 

 tance. Only two families are here recognised, one containing the 

 so-called Green'Pigeons, the other the rest of the South African 

 representatives of this Order. 



Key of tlie Genera. 



A, Fourteen tail-feathers ; plumage green and 



yellow Vinago, ]). 156. 



B. Twelve tail-feathers ; plumage never green and 



yellow, 



