356 REPTILIA. 



1. Chelonia (Tortoises and Turtles). 



2. Ophidia (Snakes). 



3. Lacertilia (Lizards). 



4. Crocodilia (Crocodiles and Alligators). 



5. Ichthyopterygia. 



6. Sauropterygia. 



> Recent. 



7. Anomodontia. 



> Extinct. 



8. Pterosauria. 



9. JDeinosauria. 



As regards their general distribution in time, the Reptilia 

 attained their maximum of development in the Mesozoic 

 period, which has hence often been called the "Age of Reptiles." 

 If the Elgin Sandstones, containing the remains of Telerpeton 

 and Stagonolepis, be of Triassic age as seems almost certain 

 then no Reptile has as yet been discovered in the Devonian 

 Rocks. In the Carboniferous Rocks, the place of the true 

 Reptiles seems to have been taken by the Amphibian group of 

 the Labyrinthodonts. It is possible, however, that the little 

 Hylonomus, of which three species were discovered in the Coal- 

 strata of Nova Scotia by Dr Dawson, may be Lacertian in its 

 affinities. It is also possible that the vertebrae from strata of 

 the same age described by Professor Marsh under the name of 

 Eosaurus Acadiensis, may belong to a marine reptile allied to 

 Ichthyosaurus. In the Permian Rocks the first undoubted 

 Reptilian remains occur, the Protorosaurus of this period being 

 probably a Lacertilian. 



Throughout the whole Mesozoic series, Reptilian remains 

 are abundant and belong to numerous and strange types. 

 Chelonians and true Crocodiles, with Lizards allied to existing 

 forms, make their first appearance in deposits belonging to this 

 period. The extinct orders of the Ichthyopterygia, Saurop- 

 terygia, Anomodontia, Pterosauria, and Deinosauria, not only 

 first appear in Mesozoic deposits, but are exclusively confined 

 to rocks of this age. In the Tertiary period, lastly, the 

 remains of Reptiles are comparatively rare, and the number 

 of types is much reduced. The living order of the Ophidia, 

 however, makes its first appearance in the Tertiary deposits. 

 In the following view of the characters and distribution in time 

 of the orders of the Reptiles, it will be advisable to consider 

 the recent orders first, though this is not in accordance with 

 their natural arrangement. 



ORDER I. CHELONIA. The first order of living Reptiles is 

 that of the Chelonia, comprising the Tortoises and Turtles, and 

 distinguished by the following characters: There is an osseous 

 exoskeleton which is combined with the endoskeleton to form 



