I S3 5. 



BIRDS. 



379 



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 

 3. Geospiza parvula. 



2. Geospiza fortis. 

 4. Certhidea oliva^ea. 



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 



