CHAP, xviii.] BIKDS. 337 



found in the Andaman and Mcobar Islands ; in the Philippines, 

 Gilolo, and the smaller Papuan Islands, and in Japan ; yet not in 

 any of the large Malay Islands or in Australia. The other genus, 

 Calcenas, consists of but a single species, yet this ranges from the 

 Mcobar Islands to New Guinea. It is not, however, as far as 

 known, found on any of the large islands, but seems to prefer 

 the smaller islands which surround them. We here have the 

 general preference of pigeons for islands, further developed in 

 these two genera into a preference for small islands ; and it is 

 probable that the same cause the greater freedom from danger 

 has produced both phenomena. 



Of the geological antiquity of the Columbse we have no evi- 

 dence ; but their wide distribution, their varied forms, and their 

 great isolation, all point to an origin, at least as far back as that 

 we have assigned as probable in the case of the Parrots. 



Order V. GALLING. 

 FAMILY 86. PTEEOCLID^E. (2 Genera, 16 Species.) 



GENERAL DISTRIBUTION. 



The Pteroclidae, or Sand-grouse, are elegantly formed birds with 

 pointed tails, and plumage of beautifully varied protective tints, 

 characteristic of the Ethiopian region and Central Asia, though 

 extending into Southern Europe and Hindostan. Being pre- 

 eminently desert-birds, they avoid the forest-districts of all these 

 countries, but abound in the most arid situations and on the 

 most open and barren plains. The distribution of the genera is 

 as follows : 



Pterocles (14 sp.), has the same range as the family ; Syrrhap- 

 tes (2 sp.), normally inhabits Tartary, Thibet, and Mongolia to 

 the country around Pekin, and occasionally visits Eastern Europe. 

 But a few years back (1863) great numbers suddenly appeared in 



