P R E F A C E. 
Apter several unsuccessful attempts to unravel the confused history of the Gigantic 
Land-Tortoises, I had to resume their investigation in the year 1872 on the receipt of a 
consignment of remains of the extinct Tortoises of the Mascarenes from L. Bouton, Esq., 
of Port Louis. Having then ascertained, with the aid of these remains (fragmentary 
as they were), that the osteology of these animals formed the safest guide to their 
study, I continued to investigate the subject in that direction, and in 1874 con- 
sidered my researches sufficiently advanced to begin their publication with a memoir on 
the Races of the Galapagos Archipelago, which appeared in vol. clxv. of the ' Philo- 
sophical Transactions.' Whilst prej)aring for publication the account of the races 
inhabiting islands of the Indian Ocean, the following most important materials 
reached me, by which entirely new facts came to light, and by which I was enabled 
to correct some of the views expressed in my first paper : — 
1. A pair of adult examples, undoubtedly natives of Aldabra, obtained through the 
mediation of the Hon. Sir Akthue H. Gordon, K.C.M.G., then Governor of Mauritius. 
2. The entire series of the remains of the Tortoise of Rodriguez, collected for the 
Royal Society by H. H. Slater, Esq. (one of the naturalists accompanying the 
" Transit-of- Venus " Expedition), and transferred by the Council of the Royal Society 
to the British Museum. 
3. A large series of the remains of the extinct Tortoises of Mauritius, collected by 
the Hon. E. Newton, and kindly placed by him in my hands for examination, 
4. The examples of the Tortoises of Albemarle and Abingdon Islands, collected by 
Commander Cookson, of H.M.S, ' Peterel.' 
The results of my examination of these materials were originally embodied in two 
memoirs — one read before the Royal Society on January 25, 1877, the other before the 
Zoological Society on February 6th of the same year, both being accepted by those 
Societies for publication in their ' Transactions.' Thinking it, however, more convenient 
