1835.] DISTRIBUTION OF ORGANIC BEINGS. 389 



hurried from it ; but I ought, perhaps, to be thankful that 

 I obtained sufficient materials to establish this most 

 remarkable fact in the distribution of organic beings. 



The inhabitants, as I have said, state that they can 

 distinguish the tortoises from the different islands ; and 

 that they differ not only in size, but in other characters. 

 Captain Porter has described* those from Charles and from 

 the nearest island to it, namely. Hood Island, as having 

 their shells in front thick and turned up like a Spanish 

 saddle, whilst the tortoises from James Island are rounder, 

 blacker, and have a better taste when cooked. M. Bibron, 

 moreover, informs me that he has seen what he considers 

 two distinct species of tortoise from the Galapagos, but he 

 does not know from which islands. The specimens that 

 I brought from three islands were young ones ; and prob- 

 ably owing to this cause, neither Mr. Gray nor myself 

 could find in them any specific differences. I have remarked 

 that the marine Amblyrhynchus was larger at Albemarle 

 Island than elsewhere ; and M. Bibron informs me that he 

 has seen two distinct aquatic species of this genus ; so that 

 the different 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. parvuhcs ; and all from 

 James and Chatham Islands (between which two other 

 islands are situated, as connecting links) belonged to l\f. 

 melanotis. These two latter species are closely allied, and 

 would by some ornithologists 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 separate islands. If the dilterent 

 islands have their representatives 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 perfectly gradu- 

 ated series in the size of their beaks. Two species of tli' 

 sub-group Cactornis and two of Camarhymhus, wei- 



* "Voyage In the U.S. %\\\^ Essex^" vul. i. p. aij. 



