
1891. Geography and Travel. 905° 
difference of the species. If one or the other of the species dies out, 
we can have, for instance : 
E E E o —cx f(x)—adx f(x) 
2d island, o — b 4 f(x) — 0 —d x f(x) 
3d island, ol o —c+ f(x) — o 
This, I think, will be sufficient to express my opinion on the differ- 
entiation of such genera which contain more than one species. 
. Now some words about the birds themselves. Creagrus, of which, so 
far as I know, only four specimens exist in the museums, has been 
considered a very rare bird ; all the authentic specimens of which have 
been collected at Dalrymple Rock, west of Chatham. This bird is 
quite common here. Wé have seen it near Freshwater Bay, Chatham, 
between Charles and Hood, and found it in considerable numbers on 
the rocks in Gardner Bay, and on Gardner Island, near Hood, in 
hundreds of specimens ; it was seen on Brattle, where many specimens 
were collected ; it was also found on a rock north of Sullivan Bay, 
ames, and on the Seymour Islands, north of Indefatigable. Creagrus 
is probably found on every steep rock which contains holes, in which 
the bird breeds. 
On Albemarle, from which island only a few species of birds were 
known, we found over forty species (South Albemarle), a number 
greater than ever recorded from any island. Geospiza magnirostris, 
not observed since Darwin, was found on South Albemarle and Jervis; 
it is simply the representative of G. strenua of other islands, as 
G. conirostris is the representative of this form on Hood. 
I will conclude this letter with a few words about the reptiles. Of 
Tropidurus I have already spoken. Geckos were found in great 
numbers on Charles (one species, G. galapagoënsis), on Albemarle, and 
on Chatham. Snakes I observed on Hood (one specimen collected), 
Barrington, and Albemarle. Conolophus exists in great numbers on 
Barrington and the Seymour Islands, but was not noticed on Any of the 
others. Amblyrhynchus is found on all islands, but is rare on some ; 
on Charles only two specimens were seen. 
The land tortoises are extinct on Charles, Chatham, Barrington, 
and Jervis, on which islands they formerly existed. They are probably 
extinct on Hood, on which a thorough search of two days over the 
whole island was without result. They are said to still exist in reduced 
numbers on James (an examination of two days was without result) and 
on Indefatigable. On South Albemarle, where we remained twenty 
days, we found the land tortoises still in considerable numbers, but it is 

