GIGANTIC TOETOISE FEOM MADAGASCAR. 309 



skeleton with which to compare), and have come to the conclusion that the differences 

 between specimens B and C may, provisionally at least, be ascribed to both age and sex. 

 On comparing the caudal vertebrae of a young Galapagos tortoise [T. elephantopus) with 

 those of an adult of a closely allied form {T. vicina) I find the articular facets to be 

 nearly plane in the former, whereas the cup-and-ball system is strongly developed in 

 the latter. As to the anchylosis or non-anchylosis of the costoids, I think the 

 examination of more material would reveal a great amount of individual differences 

 on this point, irrespective of age or sex. Both specimens of T. elephantina show no 

 trace of suture, but I find a great amount of individual variation in other species. In 

 the adult specimen of T. vicina most of the costoids show a distinct suture with the 

 centrum, whilst those of the 6th vertebra, the right one of the 10th, the left of the 

 16th and 17th, and the right of the 18th and 19th are more or less completely united 

 with the centrum. 



After describing the tail of the adult male T. elephantina, Dr. Giinther adds : — 

 "Nearly always the animal carries it [the tail] bent sidewards under the carapace, 

 generally towards the left side ; and therefore I anticipated to find a want of symmetry 

 in some portion of the root of the tail ; however, nothing of the kind can be observed." 

 This statement is not quite correct. Since the above lines were written, Dr. G. Smets ' 

 has pointed out that the basal caudal vertebrae of T. sulcata and other Land-Tortoises 

 are characterized by a remarkable asymmetry, especially with regard to the zygapo- 

 physes, and I find his statement borne out by the gigantic species as well. Smets 

 remarks of T. sulcata that the right postzygapophysis of the first sacral vertebra is 

 obliterated, whilst the left is well developed ; on the second sacral the left zygapophysis 

 is more developed than the right ; likewise on the first caudal. On the second caudal 

 the right postzygapophysis is slightly more massive than the left, but its articular 

 facet is smaller ; in the 3rd, 4th, and 5th the right postzygapophysis is more developed 

 than the left, whilst in the 6th to 8th it is the reverse. The first and second caudal 

 vertebrae have the diapophyses more developed than the left ; on the third vertebra the 

 left diapophysis is less massive but a little longer than the right ; fourth and fifth with 

 the left, seventh with the right, diapophysis longest. From the ninth vertebra any 

 striking asymmetry ceases. 



In the large male specimen described by Giinther ^ the second sacral vertebra has 

 but one prezygapophysis, the left ; the facet of the right postzygapophysis of the first 

 caudal is much larger than that of the left, but little larger in the second ; in the third 

 vertebra the left postzygapophysis is the largest, and in the fourth it is the right. In 

 the female specimen the asymmetry is much less marked. 



In the 3rd and 4th vertebrae of specimen A of T. grandidieri the right postzygapo- 

 physis is more developed than the left, in the 6th the left. 



In specimen B the left postzygapophysial facet of the second sacral is much higher 

 ' Museon, 1887, p. 394. - Ojh eit. p. 29. 



