666 ZOOLOGY. 



that a few of the Echinoderms belong to genera which flour- 

 ished in the Cretaceous Period ; so tliat in a sense the abys- 

 sal fauna may be said to be an extension in time of the 

 Cretaceous fauna ; the physical features of the deeper parts 

 of the sea having remained nearly the same, while the 

 shallower parts have risen and fallen so as to undergo great 

 changes, and have wrought corresponding changes in the life 

 along the shores of the continents. 



The following tabular view of the chief zoological faunas 

 of the earth, proposed by Mr. J. A. Allen, is based on a 

 study of the mammals, but will primarily apply to most 

 land animals. The arctic realm is most distinctly charac- 

 terized by the distribution of marine invertebrates, when it 

 becomes of primary value : 



I. Arctic realm, undivided. 



II. North Temperate realm, with two regions, viz. : 



1 . American region, with four provinces, viz. : 



a. Boreal. 



b. Eastern. 



c. Middle. 



d. Western. 



2. Europfeo-Asiatio region, also with four provinces, viz. : 



a. European. 



b. Siberian. 



c. Mediterranean. 



d. Manchurian. 



III. American Tropical realm, with three regions, viz. : 



1. Antillean. 



2. Central American. 



3. Brazilian. 



IV. Indo African realm, with two regions, viz. : 



1. African region, with three provinces, viz. : 



a. Eastern. 



b. Western. 



c. Southern. 



