PREFACE. 



The second and concluding part of the ' Catalogue of the Marine Reptiles of the 

 Oxford Clay ' begins with an account of the Pliosauridae, which were known only by 

 scattered fragments until the discoveries of Mr. Alfred N. Leeds. They are now 

 exactly denned and described, and the gigantic species, Pliosaurus ferox, proves to be 

 especially interesting. Among other features it will be noticed that in this reptile 

 the bones of the young are comparatively dense, while in old individuals they are as 

 light and spongy in texture as those of the larger existing whales. 



The marine crocodiles of the families Teleosauridse and Geosauridse, which are also 

 described in a more exhaustive manner than has previously been possible, are 

 represented by numerous skeletons and parts in an unusually good state of preser- 

 vation. As the bones have been completely removed from the clay, they can be 

 separately studied, and the collection thus adds in a remarkable degree to our 

 knowledge of the Upper Jurassic genera hitherto depending mainly on the skeletons 

 embedded in the hard Lithographic Stone of Germany and France. One of the finest 

 of these skeletons, showing impressions of the skin, is preserved in the Museum and 

 shown in the Frontispiece of the present volume. 



The value of the Catalogue is much enhanced by the careful drawings and 

 diagrammatic sketches, which have been prepared by Miss Gertrude M. "Woodward. 



A. SMITH WOODWARD. 



Department of Geologt, 



British Museum; (Natural History), 



4th February, 1013. 



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