PRESIDENTS ADDRESS. 17 



of four feet. Another equally large, but now extinct species, 

 inhabited the Mascarene Islands. 



There is no evidence of the presence of the Order Chelonia in 

 the Palaeozoic beds, its earliest appearance dates from the Upper 

 Trias. The Keuper beds of Suabia have furnished the carapace 

 of a fresh-water Pleurodira, Proganochelys and in the Rhaetian 

 beds of the Alps and England, and a marine Turtle Psephoderma. 

 Chelonia appear in great numbers both in genera and species 

 in the Upper Jurassic beds. Lydekker divides the Order into 

 two sub-orders, Athecata and Testudinata, the first group shows 

 the nearest approximation to other Reptiles and is consequently 

 the most generalized of the Order. The second group includes 

 by far the greatest number of this sub-order. It is characterised 

 by the median region of the carapace, consisting of bony-plates, 

 which are firmly attached both to the neural-spines of the vertebrae 

 and to the ribs from which they are primarily developed. The 

 Upper Jurassic yields several remains of Plesiochelys, a Pleurodiran 

 with a strongly ossified carapace differing from those now living, 

 by the weak attachment of the plastron to the carapace. The 

 Order Chelydridos is represented by Platychelys, in which the 

 characters of Cryptodira and Pleurodira appear to be united. 

 The occurrence of a marine Chelone (Chitracephalus] in the 

 Wealden Beds of Bernissart, Belgium, is an instance of their 

 power of adaptation to new conditions, such as a change from a 

 marine to a fresh-water life. Plesiochelys already mentioned, 

 appears to have survived from the Jurassic to the Wealden and 

 Purbeck periods, and to have been supplanted by Pleurosternum, 

 to which it is closely allied. Tretosternum, also from the English 

 Purbeck and Wealden, and the Belgian Wealden, has no 

 mesoplastron. The Upper Cretaceous Beds of North America 

 are far richer in Chelonia than those of Europe. They 

 did not make much progress during the older Eocene 

 period, as compared with the Cretaceous. The Trionychidae are 

 found in the Eocene Beds of the Isle of Sheppey, and in the 

 Paris Basin. North America has furnished the most ancient 

 land-Tortoise, Testudo Nebrascensis, which has been found in the 



