1835. BIRDS. 879 
differing from the Progne purpurea of both Americas, only in 
being rather duller coloured, smaller, and slenderer, is consi- 
dered by Mr. Gould as specifically distinct. Fifthly, there are 
three species of mocking-thrush—a form highly characteristic 
of America. The remaining land-birds form a most singular 
group of finches, related to each other in the structure of their 
beaks, short tails, form of body, and plumage: there are thirteen 
species, which Mr. Gould has divided into four sub-groups. 
All these species are peculiar to this archipelago; and so is 
the whole group, with the exception of one species of the sub- 
group Cactornis, lately brought from Bow island, in the Low 
Archipelago. Of Cactornis, the two species may be often seen 
climbing about the flowers of the great cactus-trees; but all 
the other species of this group of finches, mingled together in 
flocks, feed on the dry and sterile ground of the lower districts. 
The males of all, or certainly of the greater number, are jet 
black ; and the females (with perhaps one or two exceptions) are 
brown. The most curious fact is the perfect gradation in the 
size of the beaks in the different species of Geospiza, from one as 
1, Geospiza magnirostris. 2. Geospiza fortis. 
3. Geospiza parvula, 4, Certhidea clivasea, 
large as that of a hawfinch to that of a chaffinch, and (if Mr. 
Gould is right in including his sub-group, Certhidea, in the main 
