THE ORNITHOSAURIA. 517 



Family Ignanodontidae : lyuanndon, Pdorosaurus, Vectisaurus. 

 Family Hadrosauridae : Hadrosaurus, Agathaumus, Cionodon, 

 Diclonius. 



IV. Order THEROPODA. 



Family Megalosauridae : Megalosaurus, Allostiurus, Ccelosaurns, 



Crensaurus, Lcelaps. 



Family Zanclodontidae : Zanclodon, Teratosaurus. 

 Family Amhisauridae : Amphisaurus, Bathygnathus, Clepsysaurus, 



Palceosawus, Tkecodontosaurus. 

 Family Labrosauridae : Labrosaurus. 



V. Sub-Order C^ELURIA. 

 Family Caeluridae : Celurus. 



VI. Sub-Order COMPSOGNATHA. 

 Family Compsognathidae : Compsognathus. 



VII. Order HALLOPODA. 

 Family Hallopodidse : Hallopus. 



Dinosaurs are to be regarded as modified Crocodiles. The living 

 Croeodilia and the Dinosauria both probably are descended from the 

 Teleosauria. The Teleosaurs which have the articular surfaces of the 

 vertebrae flat or slightly concave, make a slight approximation to 

 Dinosaurs in other parts of the skeleton, and from this Teleosaurian 

 basis all the Dinosaurs may have been evolved by differences of func- 

 tion developed in the several parts of the body. Some of the genera 

 are probably naked, others, like Potacanthus, were (as the Rev. Darwin 

 Fox, its discoverer, first pointed out) sheathed in armour only com- 

 parable to the carapace of a tortoise or armadillo. Some genera, like 

 Iguanodon, had the tail enormously developed ; while in others, 

 like some Dinosaurs from the Cambridge Greensand, the tail was 

 almost wanting. Some genera were of the ordinary quadruped type, 

 others had a kangaroo-like form and motion. But the most singular 

 structural modification is seen in Oniithopsis and allied genera, in 

 which the vertebrae are excavated by pneumatic cavities comparable 

 to those similarly placed in birds. We should class the Ichthyosauria 

 as an aquatic order in the sub-class Dinosauria, and somewhat sim- 

 plify Prof. Marsh's classification. 



Ornithosauria. The secondary strata yield between the Lias and 

 the Chalk a remarkable group of flying animals which combined 

 characters of reptiles with those of birds. They were devoid of 

 feathers, and no covering to the skin of any kind has been found. 

 They mostly possessed teeth, better developed than those of the 

 birds from the Secondary rocks ; though Ornithostoma from the Cam- 

 bridge Greensand, and some American types, like Pteranodon, were 

 toothless, like existing birds. Perhaps if the toothless forms had 

 been found first, the avian nature of these animals would never have 

 been doubted. The tail was often long; the vertebrae usually, if 



