530 Mr. G. A. Boulengeron the American Box- Tortoises. 



XXXTX. — On the American Box-Tortoises. 

 By G. A. BouLENGER, F.R.S. 



When revising the Tortoises in 1889, I felt somewhat 

 perplexed as to the taxonomic rank to assign to some of the 

 forms of the genus Cistudo which had previously been 

 described by Gray and Agassiz. With regard to Agassiz's 

 Cistudo ornata, no doubt could be entertained that it fully 

 deserves to be regarded as specifically distinct from G. Caro- 

 lina ; the other forms, owing to the insufficient material at 

 my disposal, I provisionally admitted as varieties, which, as 

 I remarked, perhaps deserved to rank as species. Dr. G. 

 Baur (' Science,' xvii. 1891, p. 190, and Amer. Natur. 1893, 

 p. 677) has since shown that the latter alternative is the more 

 correct, and pointed out various important additional characters 

 by means of which the species may be easily distinguished. 

 In the light of this latest information I have re-examined the 

 specimens in the British Museum, and fully agree with 

 Dr. Baur. Moreover, I may add that Mexico is inhabited by 

 at least two species of the genus Cistudo^ as evidenced by 

 three specimens obtained in North Yucatan by Mr. Gaumer 

 and presented to the Museum by Mr. Salvin. These speci- 

 mens are not so perfect as might be desired ; the skins have 

 been dried, and all the bones, except the skulls, are wanting. 

 Nevertheless they appear to show this difference from all the 

 described species except C. mojor^ that the digits are 

 distinctly webbed, although a bony temporal arch is absent. 

 The latter character was believed to be characteristic of the 

 genus Cistudo until Dr. Baur pointed out the presence of a 

 complete bony quadrato-jugal arch in G. major. 



We may now distinguish six species of Cistudo, for the 

 determination of which the following synopsis will be of 

 service : — 



I. Plastron completely closing the shell, with- 

 out trace of a bridge ; carapace -with at 

 least a trace of a vertebral keel ; median 

 fingers with three phalanges. 



A. Digits shortly but very distinctly webbed ; 

 upper jaw notched in the middle, bi- 

 cuspid. 



A bony temporal arch 1. C. major, Ag. 



No bony temporal arch ; quadratojugal bone 

 vestigial 2. C yucatmia, Blgr. 



