510 MR. 0. SALVIN ON THE GALAPAGOS AVIFAUNA. 
Strix and. Asio, Zenaida, Larus, and Spheniscus. Then those of Dendreca, Progne, 
Butorides, Nycticorax and Porzana, and, finally, Dolichonyx orizivora, Ardea herodias, 
and the Ducks, Flamingo, Gannets, Plovers, and Sandpipers, though of these last a 
constant stream of immigrants may have been maintained from the earliest times. It 
must be remembered, however, that no precise order of immigration can be absolutely 
laid down, even approximately ; for one term in the proposition is an absolutely unknown 
quantity. We know nothing of the rate of change that has taken place in any one 
species, Outward circumstances may have acted upon one species so as to leave it little 
changed in a given time, whilst in the same time another species may have assumed 
distinctive generic characters. Viewing the very peculiar physical characters possessed 
by these islands when contrasted with the neighbouring American shores, it would seem 
reasonable to consider that the rate of change demanded of an immigrant species would 
be high ; consequently the origin of the islands need not be dated back to a more 
distant period than seems indicated by their volcanic origin. But I am writing of the 
Birds alone; other forms of life found in these islands present far more complex 
problems for solution, into which I am not prepared to enter. 
DESCRIPTION OF THE PLATES, 
. PLATE LXXXIV. 
Outline Chart of the Galapagos Islands, taken from the Admiralty Chart, No. 1375. 
i The dotted line shows Dr. Habel’s route. 
PLATE LXXXV, 
Camarhynchus variegatus, p. 489: fig. 1, 3; fig. 2, 2. 
PLATE LXXXVI. 
Camarhynchus habeli, p. 490: fig. 1, ¢ ; fig. 2, 2. 
PLATE LXXXVII. 
Larus fuliginosus, p. 505: fig. 1, adult; fig. 2, immature. 
PLATE LXXXVIII. 
Figs. 1 & 3. @strelata pheopygia, p. 507. Fig. 2. Procellaria tethys, 507. 
PLATE LXXXIX. 
Spheniscus mendiculus, p. 508. 
All the figures are taken from specimens in the collection of Mr. Godman and 
myself, except those of @strelata pheopygia and Procellaria tethys, the originals of 
which are in the British Museum. 
