348 AMERICAN TESTUDINATA. Part II. 



the carapace, also project beyond the attached surface of the body. As the flat- 

 tened surface is so broad here, the bridge which connects it with the outer edge 

 of the carapace is much shorter than in the Chelydroidas, and rises more steeply, 

 but its ends are less concave, and it is broader. 



The whole shield is ossified. The arrangement of the bony plates is, in some 

 respects, quite peculiar. The costal plates are constant, eight in number ; the 

 marginal plates, too, are constant; there is one odd one at each end, one for 

 each costal, and two from the front odd one to the first of those which are 

 attached to the ends of the ribs, and one from the last of these to the hind 

 odd one, making twenty-four in all. But the vertebral row is deficient; it varies 

 in number from five to seven, the last two or three being wanting, so that the 

 upper ends of the corresponding costals meet one another, and sometimes the 

 front one is equally wanting, so that the first costals meet also. The plastron, 

 in the adult at least, is made up of only eight plates, four pairs; for there is 

 no odd one, as in all the other families of the sub-order. In consequence of 

 the absence of an odd bone in the plastron, the median suture extends without 

 interruption from one end of the plastron to the other, dividing it into equal 

 halves along the middle line. The two pairs of plates, which reach entirely 

 across the body, and are sutured to the carapace, do not make up more than 

 one third of the whole length ; they are but little longer in the body of the 

 plastron than in the bridge from thence to the carapace. The front and hind 

 pairs are both broad as well as long ; they are generally joined to the other 

 pair by a flexible hinge,^ except the hind pair in Ozotheca ; but in old age 

 these hinges are either partially or completely ossified. The middle transverse 

 suture is always thoroughly ossified, and never flexible. 



The fixed part of the vertebral column rises backward with the middle line 

 of the carapace nearly to the seventh vertebra, and thence descends steeply. 

 The tail is never long and strong enough to aid in bearing the weight of the 

 body, as it is in the Chelydroidte. In the males it is much larger and longer 

 than in the females, and terminates with a horny nail. 



The body projects farther beyond the upper part of the scapular arch than in 

 the EraydoidfB, and that arch is carried far back in descending to the jjlastron, 

 so far that the coracoid reaches across the middle transverse suture. The pelvis. 



^ The movable parts of the plastron are thus are soldered to the sides of the carapaee, while in the 



different in their composition and in their attachment Emydoids with movable plastron the hinge divides 



from those of Cistudo and Emys, inasmnch as in the whole plastron transversely into halves which 



Cinosternoidce they swing upon an immovable trans- swing upon one another, and the sides of the plastron, 



verse beam, consisting of two pairs of plates which where they meet the carapace, remain also movable. 



