VI PREFACE. 



In many instances, — as for example in that of the remarkable 

 genus Miolania, from the Tertiaries of Australia and Lord Howe 

 Island, of Psephoderma from the Trias, of Pelohatochelys from the 

 Kiineridge Clay, and other extinct forms — it has been found 

 impossible to place them with any existing families, and special 

 families have been constituted for the reception of these and allied 

 types. 



Mr. Lydekker has endeavoured to correlate as far as possible the 

 fossil with the existing forms, and to follow the same classification 

 as that adopted in Mr. Eoulenger's admirable Catalogue of the 

 Recent Chelonia, from which many of the woodcuts have been kindly 

 lent by Dr. Giinther, Keeper of the Department of Zoology, to 

 illustrate the present work. 



HENRY WOODWARD. 



Department of Geology, 

 Nov. 15, 1889. 



