PLATE II. 



By J. MANSEL-PLEFDELL. F.L-S, F.G-S. 



PLEUKOSTERNON OYATUM, 



ME first trace of a Chelonian is supposed to 

 occur in some footprints on the ripple-marked 

 surface of the Bunker-Sands, accompanied by 

 the furrows of its draggling shell ; but undoubted 

 actual remains have been found in the Lias, and 

 right through the Jurassic series, and are abund- 

 ant in the estuarine deposits of the Purbecks. There is evi- 

 dence of the existence of numerous forms of Chelonians during 

 the Cretaceous period ; their remains are frequent in the 

 Tertiaries, especially in the London clays. The Land Tortoises 

 seem to have made their first appearance in the Miocene age ; 

 the most remarkable of which is the gigantic Colossochelys 

 Atlas, which measured about twenty feet in length, and is 

 supposed to have stood upwards of seven feet high ; it comes 

 from the Upper Miocene deposits of the Siwalik Hills of 

 India. 



The largest living Tortoises are found in the Galapagos 

 Islands ; several gigantic species of Testudo formerly inhabited 



