44 GUIDE TO THE FOSSIL EEPTILES, AMPHIBIANS, FISHES. 
Wall-case 
18. 
Wall-case 
19. 
Wall-case 
19. 
represented by a well-preserved skull and other remains from 
the London Clay of Sheppey. There are also small species 
of extinct genera of true turtles in the same formation 
(e.g., Argillockdys). 
The fresh-water Chelydra , now confined to the warmer 
parts of the New World, has been discovered in the Upper 
Miocene of Oeningen, Baden (Wall-case 18). 
Sub-order 3.—Pleurodira. 
The existing Chelonia which withdraw their head by 
bending the neck sideways to rest within the margin of the 
shell, are now confined to the southern hemisphere; but in 
Tertiary times they were also common in the northern 
hemisphere. Various fragmentary remains, including shells 
of Podocnemys from the Eocene of Egypt, are exhibited in 
Wall-case 19. The most noteworthy extinct genus is the 
horned Miolania, which occurs not only in the Pleistocene 
of Queensland (Plate VII.) and Lord Howe’s Island (400 
miles distant from the Australian coast), but also in rocks of 
uncertain age in Chubut, north of Patagonia (Plate VII.). 
The tail in this reptile is armoured with thick bony rings 
like those of the extinct South American armadillo, Glyjptodon. 
As Miolania must have been a land-animal, its discovery in 
regions so remote as Australia and South America is some¬ 
times cited as one proof of the former existence of a great 
Antarctic continent uniting the lands in question. 
Sub-order 4.— Amphiehelydia. 
Most of the Jurassic and Wealden Chelonia are somewhat 
intermediate between the Cryptodira and Pleurodira, and 
have been provisionally placed in a separate sub-order. 
Among typical examples may be mentioned Pleurosternum 
from the Purbeck Beds of Swanage and Platychelys from the 
Lithographic Stone (Kimmeridgian) of Bavaria (Wall- 
case 19). 
