EOCENE CHELONIANS FROM THE SALT-RANGE. 
63 
not showing any close relationship to the Chelydidce, Hemichelys appears to be 
much more nearly allied to that family, and may be the representative of a still 
earlier type from which the latter has been derived. The preservation of an appa- 
rently still more primitive type in the Australasian region is an instance analogous 
to that of the survival of Ceratodus and other primitive forms in the same area. 
Family Chelydidce. 
Characters. — Shell covered with horny epidermal shields, and an intergular 
shield present on the plastron. 
There is considerable variation as to the number of vertebral bones in the 
carapace of the different genera. Thus, in the Australian genera Chelodina, Chelymys, 
Euchelymys, and Elseya, vertebrals are entirely absent, the only azygos bones being 
the nuchal, the supra-pygal, and the pygal. 1 In Platemys there are normally six 
such bones, but in P. raniceps the first three are wanting, 2 and in a specimen of 
P. planiceps in the British Museum there are none. In the eocene form figured by 
Owen 3 under the name of Platemys bowerbanki there are seven such bones ; the 
same number being present in the existing genera Podocnemis, Peltacephalus, and 
Sternothcerus 4 (woodcut). An incomplete mesoplastral element is present in Podo- 
cnemis, Peltocephalus, Pelomedusa, Pentonyx, and Sternothcerus , 6 while in Pleuro - 
sternum this element is complete. Peltocephalus is distinguished from all the other 
genera by the fusion of the two pygals into a single shield, as in Testudo. The nuchal 
shield is wanting in Sternothcerus, Pelomedusa, Podocnemis, and Peltocephalus. 
Some writers regard the presence of a mesoplastral bone as a family character, 
and accordingly apply the name Pelomedusidce to the group presenting this feature. 
Genus Podocnemis, Wagler. 6 
Characters. — Shell thick, with a long plastro- costal symphysis ; nuchal shield 
absent; plastron solid; vertebral bones seven in number, the first five being 
elongated, and the seventh small, rhomboidal, and wedged in between the sixth 
and seventh costals. 7 
Podocnemis indica, n. sp. nobis. 
Characters. — Carapace oval, tectiform, not keeled, and narrowed posteriorly ; 
the first vertebral shield wide, the second and third elongate, total length about 
35 inches. 
1 Riitimeyer, op. tit., p. 24. 
5 Ibid. 
3 Op. tit., pi. XXIII. 
* Riitimeyer, op. tit., p. 24. 
6 Riitimeyer, op. tit., p. 23. 
6 Syst. Amphibien, p. 135 (1830). 
7 Riitimeyer, op. tit., p. 24. 
