BIOLOGIA CENTRALI-AMERICANA. 
ZOOLOGIA. 
Class REPTILIA. 
Order CHELONIA. 
Fam. TESTUDINID. 
CISTUDO. 
Cistudo, Gray, Cat. Shield Rept. p. 39. 
1. Cistudo mexicana. | 
Cistudo mexicana, Gray, P. Z. 8. 1849, p. 16, t. ii.; Bocourt, Miss. Sc. Mex., Rept. p. 17. 
Hab. Muxtco, Tampico and Mexico city (Bocourt). 
Gray was the first who specifically separated from the common type of North-American 
Box-Tortoise a form whose hind feet are armed with three large claws instead of four. 
However, in examining the value of this character, Agassiz (Contr. Nat. Hist. Amer. 
i. p. 444) came to a different conclusion, stating that the outer toe of the hind foot 
fades away gradually; and, whilst he distinguished not less than four different species 
of Cistudo, these species included three- as well as four-toed specimens. 
In a case in which one naturalist, though he has examined many hundred specimens, 
does not feel justified in expressing a decided opinion, it would be most hazardous for 
another to do so who has much less material at hand. Yet, having seen specimens of 
Agassiz’s four species, I may be allowed to say that I incline to the belief that there is, 
in fact, one species of Box-Tortoise only, and that one of its hind toes becomes aborted 
in the south-western and southern range of its distribution. Nevertheless, I have 
considered it best to retain the name given by Gray, the more so as both the typical 
specimens are singularly distinguished by having a small additional scute intercalated 
between the fourth and fifth, so that there are six: vertebrals altogether. This, of 
BIOL. CENTR.-AMER., Rept., April 1885. *] 
