56 GUIDE TO KEPTILES AND AMPHIBIANS. 



typical South American species), differ from the Pelomedusidce by the 

 circumstance that the neck cannot be completely withdrawn into the 

 shell, and likewise by the absence of a mesoplastral element in the 

 plastron, which thus includes only nine bones. A nuchal shield, which 

 is invariably wanting in the Pelomedusidce, may be present on the 

 carapace in this family. The true Matamata {Ghelys fimoriata, 185, 

 fig. 58) is a very remarkable creature, carnivorous in habit, and passing 

 its time at the bottom of the Brazilian rivers. The shell is raised into 

 several knob-like prominences, and the skin of the neck and the 

 sides of the head are developed into a number of moss-like processes, 

 which probably serve to attract fishes within reach. On these fishes 

 and other vertebrates the Matamata feeds ; owing to the weakness of 

 the creature's jaws, it is probable that they are swallowed whole. 



Fig. 58. 





m 



The Matamata Tortoise (Chelys fimbriata) ; reduced. (No. 185) 



Hydromedusa (202), Platemys (200), Rhinemys (195), and Hydrastis 

 (192) are also South American, but the other kinds are Australasian. 

 The extinct Horned Tortoises forming the family Miolaniidce 

 (193, 194) are gigantic, and apparently Pleurodiran, species, charac- 

 terised by the presence of large flanges and prominences on the skull, 

 one pair of which resembles horns in form and position. The tail is 

 also invested in a bony armour recalling that of the Armadillos among 

 Mammals. The geographical distribution of the family is very remark- 

 able, species of the typical and only genus occurring in Australia and 

 Lord Howe Island on the one hand, and in Patagonia on the other. 



Sub-order III. — Amphichelydia (extinct). 



Family Phurosternidce. 



The extinct Oolitic Tortoises of this family, like Plevrosternum 

 lulloclci (203), resemble the living Stemothcerus among the Pelome- 



