SIDE-NECKED TORTOISES. 97 



The other two genera of the family — Pelomedusa and Sterno- 



therus — differ from the first by the absence of a bony roof to the 



temporal region of the skull, and likewise by the presence of five claws in both the 



front and hind-feet. Whereas, however, the former has the mesoplastral elements 



of the plastron small and similar to those of the greaved tortoises, in the latter 



they are as well developed as the other elements of the plastron, meeting in the 



middle line. Pelomedusa is represented by a single species common to Africa 



and Madagascar, but of the six species of Sternotherus, five are exclusively African, 



while the sixth inhabits both Eastern Africa and Madagascar. The right half 



of the upper shell of one of the species is represented on p. 90. 



A remarkable Chelonian (Carettochelys insculpta) from the Fly 

 Fly River Turtle. . v -, i . 



River, New Guinea, differs from all other members of the group, in 



the absence of horny shields on the shell and the conversion of the limbs into 



paddles, each of which carries but two claws. The neck is not retractile. In the 



carapace there are six very small neural bones, which are not in contact with one 



another, thus allowing each pair of costals to meet in the middle line ; and the 



plastron has only the usual nine bones. A wavy sculpture ornaments the whole of 



the external surface of the shell, which attains a length of about 18 inches. The 



head is large, and the tail relatively short. The species, which represents a 



separate family (Carettochelyidce), is still very imperfectly known; and it has 



been suggested that it does not belong to this group at all. It is not improbable 



that a chelonian (Hemichelys), from the Eocene rocks of India, indicates a second 



member of the same family, as its shell was similarly devoid of horny shields. 



Australian Probably the most aberrant members of the whole order were 



Horned Tortoises, certain gigantic tortoises (Miolania) from the superficial deposits of 



Australia, characterised by the presence of 



several pairs of horn-like protuberances on the 



skull, and also by the investment of the tail in 



a bony sheath, recalling that of the armadillos. 



Unfortunately, the shell of these strange reptiles 



is known only by fragments; but, from the 



conformation of the bones of the feet, we are 



FRONT VIEW OP SKULL OF HORNED TORTOISE. • 



enabled to say that they were terrestrial, while 

 the structure of the palate indicates that they were herbivorous. They clearly 

 constitute a fourth family (Miolaniidce) of side-necked tortoises. 

 Extinct European The Secondary rocks of Europe contain the remains of a number 

 Genera. £ extinct tortoises which may be referred to a fifth family (Plesio- 

 chelyidce) of the group. While agreeing with the existing Chelyidce in having but 

 nine bones in the plastron, these extinct forms differ by the much greater thickness 

 of their shells, and also by the circumstance that only one of the lower bones of 

 the pelvis is welded to the upper surface of the plastron, whereas in the existing 

 families both are thus united. Abundant in both the Oolitic and Wealden rocks, 

 the majority of these tortoises are referred to the genus Plesiochelys, although 

 some, as the one of which the carapace is represented in the figure on the next page, 

 are separated as Hylcechelys, being distinguished by the enormous width of the 

 vertebral shields, in which the breadth may be three times the length. Nothing 



VOL. V. — 7 



