CHAP. XIX.] 



EEPTILES. 



407 



little interest as regards geographical distribution. America 

 possesses both Crocodiles and Alligators ; India, Crocodiles 

 and Gavials ; while Africa has Crocodiles only. Both Croco- 

 diles and Gavials are found in the northern part of the 

 Australian region, so that neither of the three families are 

 restricted to a single region. 



Fossil Crocodilia. 



The existing families of the order date back to the 

 Eocene period in Europe, and the Cretaceous in North 

 America. In the south of England, Alligators, Gavials 

 and Crocodiles, all occur in Eocene beds, indicating that the 

 present distribution of these families is the residt of partial 

 extinction, and a gradual restriction of their range — a most 

 instructive fact, suggesting the true explanation of a large num- 

 ber of cases of discontinuous distribution which are sometimes 

 held to prove the former union of lands now divided by the 

 deepest oceans. In more ancient formations, a number of 

 Crocodilian remains have been discovered which cannot be 

 classed in any existing families, and which, therefore, throw no 

 light on the existing distribution of the group. 



Order V.— CHELONIA. 



Family 57.— TESTUDINIDyE. (14 Genera, 126 Species.) 



General Distkibution, 



Neotropical Ne arctic Pal^arctic Ethiopian I Oriental Australian 

 Si;b-regions. Sub-regions. Sub-regions. Sub-region.s. Sub-regions. Sdb-begions. 



1.2.3.4 i 1.2. 3. 4 1.2—4 '< 1.2.3.4 1.2.3.4 



The Testudinida?, including the land and many fresh-water 

 tortoises, are very widely distributed over the Old and New 

 worlds, but are entirely absent from Australia. They are 

 especially abundant in the Nearctic region, as far north as 

 Canada and British Columliia, and almost equally so in the 



