308 ME. G. A. BOULBNGEB ON AN EXTINCT 



The mandible has a double denticulate ridge, between which the alveolar surface is 

 deeply concave ; its outer surface slopes outwards and is concave ; the symphysis is 

 short and without a backward dilatation of the lower margin. 



3. Cervical Vertebrw. — Among the remains mentioned by Vaillant was a third 

 biconvex cervical vertebra, thus affording a valuable diagnostic character confirming 

 the deductions arrived at from the examination of other bones. Our material is, 

 unfortunately, very scanty, consisting merely of two second vertebrae, one sixth, one 

 seventh, and three eighth, one of the latter being reduced to the arch. I have there- 

 fore no special remarks to offer on this part of the skeleton. 



4. Sacral and Caudal Vertebrw. — A great number of vertebrae were collected, which 

 I have been able to sort out and refer to three specimens, as follows : — 



A. The largest specimen : 7 vertebrae, referable to the 3rd, 4th, 6th, 10th, 11th, 12th, 

 and 13th caudals. In all these the arch is anchylosed to the centrum, and so are the 

 costoids to the vertebrae. I regard this specimen as a male. 



B. A smaller specimen, with centrum and arch and costoids likewise anchylosed, but 

 the arch less elevated and less produced posteriorly ; the series consists of a sacral 

 and 11 caudal vertebrae, viz. 1st and 2nd, 4th and 5th, and 7th to 13th. I regard this 

 specimen as a female, probably the same as yielded the shell and skull which were 

 found associated. 



C. This specimen, which agrees nearly is size with the preceding, differs in having 

 the centra thicker and joined by suture to the arches, which in some of the vertebrae 

 have even become detached ; the costoids were also loosely attached and have been 

 lost. These vertebrae form a complete series from the 2nd to the 18th. 



The bones in specimens A and B agree so well with those of T. elephantina, male 

 and female respectively, that I have no doubt they belong to the same form as yielded 

 the skull described above. As regards specimen C, there are, on the other hand, 

 several differences, so that I have to consider whether they are referable to the same 

 species. These differences consist chiefly in the greater vertical diameter of the 

 centrum, the lesser excavation of the articular cavity, the persistent suture between 

 arch and centrum in the anterior vertebrae, 8th inclusive, and the autogenous costoids 

 throughout. 



Owing to the fact that the vertebrae are nearly equal in size in specimens B and C it 

 would seem, at first, that age cannot be made to account for the differences. However, 

 we must bear in mind that the tail differs so much in size according to the sexes in 

 these Tortoises that it may be as large in a half-grown male as in a full-grown female 

 of the same species ; and how great the differences in the shape of the bones are may 

 be gathered from a perusal of Giinther's descriptions on pp. 29 and 37 of his memoir, 

 which deal with what I regard as male and female of one and the same species. I have 

 therefore carefully compared the caudal vertebrae of the adult male T. elephanti7ia with 

 those of the female of the same species (I regret to have no half-grown or young male 



