276 



GALAPAGOS ARCHIPELAGO. 



[CHAP, xvn 



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 



. Geospiza magnirostris, 

 3. Geospiza parvula. 



a. Geospiza fortis. 



4. Certhidea olivacea. 



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 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 

 group), even to that of a warbler. The largest beak in the genus 

 Geospiza is shown in Fig. i, and the smallest in Fig. 3 ; but instead 

 of there being only one intermediate species, with a beak of the size 

 shown in Fig. 2, there are no less than six species with insensibly 

 graduated beaks. The beak of the sub-group Certhidea, is shown in 

 Fig. 4. The beak of Cactornis is somewhat like that of a starling ; 

 and that of the fourth sub-group, Camarhynchus, is slightly parrot- 

 shaped. Seeing this gradation and diversity of structure in one small, 

 intimately related g r oup of birds, one might really fancy that from an 



