INTRODUCTION. 



In the present volume the account of the Plesiosauria in the Leeds Collection is 

 completed by the description of the Pliosauridue, represented by the genera Pliosaurus, 

 Simolestes, and Peloneustes. The Crocodilia are also described and catalogued, this 

 order being represented by several members of two families, the Teleosauridse and the 

 Geosauridae. The Teleosauridse include two genera, Steneosaurus and Mycterosuchus, 

 the latter being now established for the reception of the species Mycterosuchus nasutus, 

 which is in several respects less specialised for an aquatic life than the species of 

 Steneosaurus. The Geosauridae are all referred to the genus Metriorliynclms, the 

 various species being, on the whole, closely similar to one another, and there being a 

 fairly complete gradation of forms between the slender-snouted species like Metrio- 

 rhynchus Iceve and the broad-skulled and short-snouted M. durobrivense, which was 

 formerly made the type of the genus Suchodus. The family Geosauridae, as here 

 understood, agrees exactly with the group Thalattosuchia of E. Fraas. 



The Pliosauridse differ in several respects from the Elasmosauridae, described in 

 Part I., the differences resulting for the most part from their greater adaptation to a 

 pelagic life. As pointed out in the Introduction to Part I. (p. xv), the Elasmosaurs, 

 with their long neck and small head, probably paddled about on the surface of the 

 water of no great depth, the elongation of the neck being ill-adapted for rapid motion 

 beneath the surface, but of great advantage in procuring food. In the Pliosaurs, on 

 the other hand, the cervical vertebrae are not only fewer in number but possess 

 relatively shorter centra than are found in the Elasmosaurs. At the same time, their 

 head was proportionately larger, and in Pliosaurus and Peloneustes at least had a long 



