Dr. J. E. Gray on the Family Chelydradai. 69 



from that figure to be distinct from Stauremys ; but in his 

 last paper Mr. Cope has enlarged Claudius and placed my 

 Stauremys as a section of it, and refers Staurotypus to a dif- 

 ferent family. 



He divides the specimens described into two species on 

 account of the difference of the size of the head ; but this is 

 common to many terrapins, and appears to be a sexual cha- 

 racter, or one liable to occur in specimens from the same 

 locality. 



Section II. Eurysterna. (Trap Terrapins.) 



The sternum covered with five pairs of shields, and gene- 

 rally a small odd or gular shield, formed of the rudiments of the 

 two geminate front shields, between the fore parts of the front 

 lateral pair. The sternum without any odd internal or meso- 

 sternal bone, which is found in all the other Chelonians. The 

 lateral pair of bones united together by a linear cross suture 

 and by a dentate central longitudinal suture, forming a square 

 disk which is covered by the abdominal pair of plates, the 

 anterior and posterior pairs being very broad and united by a 

 central longitudinal suture, and each being united to the front 

 and back of the central abdominal portion by a more or less 

 straight transverse suture at each end, which allows the front 

 and hinder portions to be movable on the central one. The 

 front portion is covered externally with two pairs of plates 

 and the odd anterior one when present ; the hinder portion 

 with two pairs of plates. 



The general structure of these terrapins is peculiar j the 

 marginal plates are produced up to meet the dilated ribs. 

 Indeed the whole osteology of this group deserves a mono- 

 graph ; and I only regret my inability to undertake it. 



The only very young one that I have seen of this group 

 leads me to suppose that the bones in the young state form a 

 very broad ring, leaving a central longitudinal space between 

 them, which becomes filled up as the animal grows ; and 

 in the adult state these bones are all united together, forming 

 a most solid bone, which, in the more developed genera, is 

 divided by two cross sutures so as to have a movable flap at 

 each end. 



This division was accidentally left out in the Hand-list of 

 Tortoises in the Museum, at p. 57. 



(In the account of the development of the sternum of Che- 

 lonians in the ' Annals,' xi. p. 163, I see that, by a mistake 

 of the amanuensis, the front flap is said to consist " of the 

 frontal pair of bones and the odd bone." It ought to be " and 

 no odd bone.") 



