1897.] The Origin of the Galapagos Islands. < 889 
from the Atlantic, and the whole African portion of the Indian 
Ocean. The Hydrophide extend north to Japan, south to 
Tasmania and New Zealand; east to the west-coast of Amer- 
ica from Mexico to Ecuador. Only one species is found on 
this coast Hydrus platurus Linn.; recorded from Salina Cruz, 
Mexico; Panama; and off the coast of Ecuador. 
This family is certainly younger than Miocene, since no 
members of it, are found in the Westindian Sea. It probably 
became much differentiated after the formation of the Indo- 
pacific Ocean. 
The geographical distribution of different genera of Birds on the 
Pacific Islands. 
Let us consider the distribution of different genera of 
the COLUMBIA. Our knowledge of the fossil Columb com- 
mences with the lower miocene of Allier in France, Columba 
calcaria Miln. Edw. The very peculiar group, represented by 
the Dididæ (Didus and Pezophaps) from the Mascarene Is- ' 
lands, Mauritius and Bourbon, were exterminated long ago. 
Living specimens of (Didus ineptus) were seen as late as in 
1679 ; of Pezophaps solitarius (the Solitaire) in 1761. 
The Columbide are certainly geologically an.old group. 
Family TRERONID#. 
Subfamily Ptilinopodine. 
Distribution of the genus Ptilinopus Swainson, 1825 (from 
Salvadori). 
1. Ptilinopus flavicollis Finsch & Hartl. Timor and Flores. 
2. Ptilinopus xanthogaster Wagl. Banda, Khoor, Ké, Tenim- 
ber Islands, Damma Island, and Lettie. 
3. Ptilinopus ewingi Gould. Northern Australia from Port 
Essington to Cape York. 
4. Ptilinopus swainsoni Gould, Eastern Australia from Cape 
York to New South Wales, the Islands in Torres Strait and 8. 
E. New Guinea. 
+? Salvadori T. Catalogue of the Columbe or Pigens in the collection of the 
British Museum, p. 83-112. London, 1893. Catalogue of the Birdsinthe British 
Museum, vol. XXI. London, 1898. oe 
