392 REPTILIA ORDER 2L CHELONIA. 



invested with separate horny shields, in the leathery turtle it is composed of 

 a vast number of minute irregular ossifications, fitting together like mosaic, 

 and having no sort of connection with the internal skeleton, while its investi- 

 ture takes the form of a continuous leathery skin. Seven bold longitudinal 



ridges traverse the upper shell 

 from end to end, and there are 

 five similar ridges on the under 

 shell, which is less fully developed, 

 Claws are totally wanting on the 

 flippers, of which the front pair 

 greatly exceed the hinder in 

 length. Although the structural 

 peculiarities of the skull are of the 

 highest importance in determin- 

 ing the systematic position of the creature, they need not be further 

 alluded to in this place. In length this turtle frequently exceeds six 

 feet. The leathery turtle, which is now rapidly diminishing in numbers, is 

 an inhabitant of the wanner oceans, one of its favourite haunts being the 

 Tortugas Islands off the Florida coast. It is known to be carnivorous, and 

 its habits are probably very similar to those of the true turtles. Com- 

 mercially this species is of no value, its flesh having a strong and highly un- 

 pleasant taste of musk. 



Sub-Order II Pleurodira. 



The members of the second sub-ordinal group of the Chelonia are best dis- 

 tinguished externally by the mode in which they withdraw the head and neck 

 into the shell. In place of the S-like movement characterising the preceding 

 group, these tortoises always bend the neck to one side in a horizontal plane, 

 so that instead of occupying the middle of the front aperture of the shell, the 

 head when retracted lies more or less on one or the other side, according to 

 the relative length of the neck. This very obvious characteristic is, however, 

 by no means the sole claim of the group to distinction. If the dried skull be 

 examined, it will be found that the bony ring surrounding the aperture of 

 the ear is entire instead of being notched behind, and also that the lower 

 surface of the quadrate-bone is hollowed in order to receive a knob on the 

 articulating portion of the lower jaw. In all cases the upper and lower shells 

 are fully ossified and closely joined ; and both have a firm union with the 

 bones of the pelvis. When horny shields are present at all, there is invari- 

 ably an intergular between or behind the two gulars. The Pleurodira are 

 now restricted to the Southern Hemisphere, and are the only tortoises in- 

 habiting Australia and Papua*- 



The first family of the sub-order is represented by eight generic types, all 

 of which are restricted to South America and Australasia. As distinctive 



features of the family, may be mentioned the presence of 



Family only nine bones in the lower shell, the incapacity of com- 



Chelyidce. pletely retracting the neck within the margin of the carapace, 



and the absence of the so-called temporal bony arch on the 

 sides of the skull. The typical member of the family is the grotesque mata- 

 mata (Chelys Jimbriata) of the Guianas and North Brazil, a species easily 

 recognised by its flattened triangular head, the peculiar tuft-like fifaments on 

 the sides of the broad and long neck, and the great bosses formed by the 



