66 
TORTOISES AND TURTLES. 
Hinged The third genus of this group ( Cyclemys ), which is confined to 
Terrapins. India, Malayana, and the south of China, is represented by some 
half a dozen species, which, while agreeing with the members of the foregoing 
genus in the presence of a bony temporal arch to the skull, differ by having a 
well-marked transverse ligamentous hinge across the middle of the plastron, 
whereby its hinder lobe is rendered movable, and capable of more or less com¬ 
pletely closing the posterior aperture of the shell. None of the species have a 
shell of more than 8 inches in length. The genus may be subdivided into two 
groups, each containing three species. In the former, as represented by 0. dhor y 
of Northern India and the Malayan region, the plastron, which is notched behind, 
cannot completely close the shell; while the hinder margin of the carapace is 
serrated. In the second group, on the other hand, of which the Amboyna hinged 
terrapin (C. amboinensis ) is a familiar example, the plastron is capable of 
completely closing the hinder aperture of the shell, while the posterior margin 
CHAIBASSA TERRAPIN (§ hat. size). 
of the carapace is not serrated. These species also have the shell keeled on the 
back in the young state. In the Amboyna species, as also in C. flavomarginata , 
the hinder end of the plastron is entire, although in a third (C. trifasciata ) it 
is notched. 
Box-Tortoises. Agreeing with the hinged terrapins in the presence of a trans¬ 
verse ligamentous hinge across the middle of the plastron, by the aid 
of which the openings of the shell can be closed, the two North American species 
of box-tortoises, together with all the remaining members of the family, differ 
from the former in that the hexagonal neural bony plates of the carapace have 
the shorter of their two lateral surfaces placed anteriorly, instead of posteriorly, 
this arrangement being shown when the shell is stripped. The presence of 
the hinge in the plastron serves to distinguish the box-tortoises from all the 
members of the second group, with the exception of the pond-tortoises, while from 
the latter they are separated by the beak being hooked, and the absence of a bony 
temporal arch to the skull. In the box-tortoises the head is covered with smooth 
skin above, tne toes having only a rudimental web, and the tail is short. The 
Caiolina box-toitoise ( Cistudo ccLTolinct ) is a somewhat variable species as regards 
size, the length of the shell ranging from a little over 4 to somewhat more than 
5 inches. The highly convex carapace is almost hemispherical in shape, and is 
