306 PALEONTOLOGY. 



periods: their numbers became greatly diminished in the 

 cretaceous stages ; and in the tertiary strata we find the 

 remains of only crocodiles and alligators. 



The saurians exhibit, therefore, an order of decadence from 

 the oolitic period down to the present ; for we cannot for a 

 moment compare the Crocodiles, Manatis, Iguanas, and 

 Lizards, of our day, with the enormous reptiles that basked 

 on the shores, and swam in the waters, that trod the earth, 

 and flitted through the air, during the oolitic and wealden 

 periods. 



We have seen that the Saurians form six families ; of 

 these, four are now entirely extinct, and two only are living 

 the Crocodilidse and the Lacertinida3. 



Of the extinct families, the MEGALOSAIIEIDJE lived along 

 the shores of ancient rivers, from the great oolite to the 

 neocomian stages. 



The LABYKI^THIDJE were gigantic frog-like reptiles of like 

 littoral habits, and were special to the triasic period. They 

 have left their huge foot-marks on the muddy shores, and 

 their bones in the Keiiper strata of that period. 



The ICHTHYOSATJKLDJB were organised solely for an aquatic 

 life : they ranged from the triasic to the oolitic periods, but 

 had their greatest development in the lias. 



The PTEKODACTYLID^ differed from all other families either 

 living or extinct in the structure of their anterior extremities, 

 which were at once feet and wings, and fitted these reptiles 

 for leading an arboreal life in the forests of the ancient land. 

 They extended their range from the lias to the wealden 

 stages, but were most abundant about the middle of the 

 oolitic period. 



The CJielonians left their foot-steps on the triasic strata, 

 and have lived in all the subsequent periods. They attained 

 their greatest development in the modern epoch. 



The Ophidians and the Batrachians were created during 

 the tertiary period, so that in reptiles and fishes, the orders 

 the most inferior in organisation were the last created of 

 their class. Whilst the saurians exhibit a decadence, the 

 ophidians and batrachians show a great increase of forms in 

 the modern epoch. 



The theory of progressive development receives no sup- 

 port from the facts unfolded by the history of fossil reptiles. 



