Vol. II, Pt. I] VAN DENBURGH— GALAPAGOS TORTOISES 259 



1. Abingdon T. abingdoni Giinther. 



2. James T. darwini Van Denburgh. 



3. Jervis T. wallacei Rothschild. 



4. Duncan T. ephippium Giinther. 



5. Indefatigable T. porteri Rothschild. 



6. Barrington T. sp. 



7. Chatham T. chathamcnsis Van Denburgh. 



8. Hood T. hoodensis Van Denburgh. 



9. Charles T. elephantopiis Harlan. 



10. Narborough T. phantastica Van Denburgh. 



11. Vilamil, Albemarle T. giintheri Baur. 



12. Iguana Cove, Albemarle T. vicina Giinther. 



13. Tagus Cove, Albemarle T. microphyes Giinther. 



14. Bank's Bay, Albemarle T. becki Rothschild. 



15. Cowley Mountain, Albemarle T. sp. 



2. DESCRIPTION. 



It next becomes necessary to investigate the differences 

 which distinguish these races of land tortoises one from an- 

 other, to endeavor to find the Hmits of their variation, and to 

 point out those characters which are available for their classi- 

 fication. This investigation we may divide into a consider- 

 ation of external characters and an examination for osteo- 

 logical dififerences. The external characters may be divided 

 into those of the shell, and those of the soft parts — the head, 

 neck, limbs, and tail. 



The Shell — Is covered with horny plates which do not 

 differ in number.^ but which vary in outline according to the 

 shape of the bony shell. In young tortoises these plates bear 

 striations corresponding to the lines of growth. Older indi- 

 viduals become smoother, but in certain races this tendency 

 seems to be developed more strongly than in others. The 

 oldest individuals of almost all races lose these striations. In 

 certain races, the central portions of the vertebral and costal 

 plates are elevated much more than in others. There are also 

 marked differences in the lateral outline of the marginal plates. 

 The upper border of the eighth marginal plate in Testudo 

 abingdoni is much shorter than in any other race. In the 

 Duncan Island tortoises one finds an occasional specimen with 

 the pectoral plates reduced in size so that they do not meet on 

 the median line. This tendency becomes more constant in 

 T. chathamensis. It is unknown in any of the other races. 



lExcept as individual variations. See T. ephippium and T. viicrophyes. 



