1C8 GALAPAGOS ARCIIIPELAGU. 



islands probably have their representative species 

 or races of the Amblyrhynchus, as well as of the 

 tortoise. My attention was first thoroughly aroused 

 by comparing together the numerous specimens, 

 shot by myself and several other parties on board, 

 of the mocking-thrushes, when, to my astonishment, 

 I discovered that all those from Charles Island 

 belonged to one species (Mimus trifasciatus) ; all 

 from Albemarle Island to M. parvulus ; and all 

 from James and Chatham Islands (between which 

 two other islands are situated as connecting links) 

 belonged to M. melanotis. These two latter spe- 

 cies are closely allied, and would, by some orni- 

 thologists, be considered as only well-marked races 

 or varieties ; but the Mimus trifasciatus is very 

 distinct. Unfortunately, most of the specimens of 

 the finch tribe were mingled together ; but I have 

 strong reasons to suspect that some of the species 

 of the sub-group Geospiza are confined to separ- 

 ate islands. If the different islands have their rep- 

 resentatives of Geospiza, it may help to explain 

 the singularly large number of the species of this 

 sub-group in this one small archipelago, and as a 

 probable consequence of their numbers, the per- 

 fectly graduated series in the size of their beaks. 

 Two species of the sub-group Cactornis, and two 

 of Camarhynchus, were procured in the archipel- 

 ago ; and of the numerous specimens of these two 

 sub-gi'oups shot by four collectors at James Island, 

 all were found to belong to one species of each ; 

 whereas the numerous specimens shot either on 

 Chatham or Charles Island (for the two sets were 

 mingled together) all belonged to the two other 

 species : hence we may feel almost sure that these 

 islands possess their representative species of these 

 two sub-groups. In land-shells this law of distri- 

 bution does not appear to hold good. In my very 



