252 HISTORICAL PALEONTOLOGY. 



that it may have occasionally visited the shore, the resem- 

 blance of its extremities to those of the Turtles may lead us to 

 conjecture: its movements, however, must have been very 

 awkward on land; and its long neck must have impeded its 

 progress through the water, presenting a strong contrast to the 

 organization which so admirably fits the Ichthyosaurus to cut 

 through the waves. " As its respiratory organs were such that 

 it must of necessity have required to obtain air frequently, we 

 may conclude "that it swam upon or near the surface, arching 

 back its long neck like a swan, and occasionally darting it 

 down at l!ie fish which happened to float within its reach. It 

 may perhaps have lurked in shoal water along the coast, con- 

 cealed amongst the sea-weed ; and raising its nostrils to a 

 level with the surface from a considerable depth, may have 

 found a secure retreat from the assaults of powerful enemies; 

 while the length and flexibility of its neck may have compen- 

 sated for the want of strength in its jaws, and its incapacity 

 for swift motion through the water. " 



About twenty species of Plesiosaurus are known, ranging 

 from the Lias to the Chalk, and specimens have been found 

 indicating a length of from eighteen to twenty feet. The 

 nearly related " Pliosaurs," however, with their huge heads 

 and short necks, must have occasionally reached a length of at 

 least forty feet the skull in some species being eight, and the 

 paddles six or seven feet long, whilst the teeth are a foot in 

 length. 



Another extraordinary group of Jurassic Reptiles is that of 

 the " Winged Lizards " or Pterosauria. These are often spoken 

 of collectively as " Pterodactyles, " from Pterodactylus, the 

 type-genus of the group. As now restricted, however, the 

 genus Pterodactylus is more Cretaceous than Jurassic, and it is 

 associated in the Oolitic rocks with the closely allied genera 

 Dimorphodon and Rhamphorhynchus. In all three of these 

 genera we have the same general structural organization, in- 

 volving a marvellous combination of characters, which we are in 

 the habit of regarding as peculiar to Birds on the one hand, to 

 Reptiles on another hand, and to the Flying Mammals or 

 Bats in a third direction. The " Pterosaurs " are " Flying " 

 Reptiles, in the true sense of the term, since they were indu- 

 bitably possessed of the power of active locomotion in the air, 

 after the manner of Birds. The so-called "Flying" Reptiles 

 of the present day, such as the little Draco volans of the East 

 Indies and Indian Archipelago, possess, on the other hand, no 



