40 VEBTEBRATA. 



earlier than the Eocene, where they were apparently numerous. 

 The genus Titanophis comprised several marine species of huge 

 size, one at least thirty feet in length (Marsh), One species of 

 serpent has been found in the Cretaceous of France. 



The reptiles may be divided into the following orders: — 



ORDERS ENTIRELY EXTINCT. 



1. Dinosaui'ia. 



2. Pterosauria (Ornithosauria). 



3. Theroraorpha. 



4. Ichthyopterygia. 



5. Sauropterygia. 



6. Mosasauria (Pythonomorpha). 



ORDERS WITH LIVING REPRESENTATIVES. 



1. Grocodilia. 



8. Lacertilia. 



9. Rhynchocephalia. 



10. Chelonia. 



11, Ophidia. 



The Rhynchocephalia includes only one living species, the 

 Hatteria or S2)henodon of ]^ew Zealand. The Triassic Rhyn- 

 chosaurus and Hyperodapedon belong here. Related to the 

 lizards, they have, however, a more primitive structure. 



ORDER DINOSAURIA. 



This group includes such a variety of forms that Professor 

 Marsh regards it as a sub-class. In 1882 he wrote as follows : 

 "The great number of subordinate divisions in the group, and 

 the remarkable diversity among those already discovered, indicate 

 that many new forms will yet be found. Even among those 

 now known there is a much greater difference in size and in 

 osseous structure than in anj^ other sub-class of vertebrates, with 

 the single exception of the placental mammals. Compared M'ith 

 the Marsupials, living and extinct, the Dinosauria show an equal 

 diversity of structure, and variations in size from by far the 

 largest land animals known — iifty or sixty feet long, down to 

 some of the smallest, a few inches only in length. 



According to present evidence the Dinosaurs were confined 

 entirely to the Mesozoic Age. They were abundant in the Trias- 



