382 ORTMAXN — DISTRIBUTION OF DECAPODS [April 3, 



III. Archiplata of von Ihering, comprising Brazil, south of the 

 Amazonas, and northern Argentina. 



IV. Archinotis, comprising Australia and Antarctica. As will 

 be noticed, the term Archinotis (as used by von Ihering and others) 

 does not exactly correspond to the meaning given to it here, but we 

 think it convenient to define this term in this way, applying it only 

 to the truly notal regions ; aside from Australia and Antarctica, a 

 part of South America belongs to Archinotis, namely the western 

 (Chilian coast range). 



Note — The existence of this ring-shaped continent Mesozonia in 

 Upper Cretaceous times is extremely important for marine zoogeo- 

 graphy. The distinction of two types of marine faunas, the Medi- 

 terranean and the Pacific, is well known among geologists, and 

 this continent furnishes an explanation for this differentiation : all 

 parts of the oceans lying to the north of Mesozonia — as far as the 

 present knowledge goes — possess the Mediterranean type, all parts 

 to the south of it exhibit the Pacific type. 1 In subsequent times 

 both types of marine faunas frequently communicated, but there 

 was never a complete fusion of both elements, and finally they 

 developed into the Atlantic and Indo Pacific types of the present 

 marine fauna, the Atlantic being a continuation of the Mediterra- 

 nean. In later Tertiary and recent times the differences of both 

 were again emphasized, chiefly on account of the development of 

 an Arctic and Antarctic type through the action of climatic 

 agencies, which prevented their communication in the northern and 

 southern regions of the earth At present both original types 

 which, as we have seen, go back to the Cretaceous, are restricted to 

 the circumtropical belt, and are absolutely separated. 



c. Lower Tertiary. (See Fig. 7, p. 383.) 



The following changes appear : 



The ring formed by Mesozonia was interrupted at three places : 

 1. between Guiana and Africa; 2. in Central America (Panama 

 region) ; 3. between Africa and Southeast Asia. This latter inter- 



1 Of course, there are apparent exceptions. The Lower Senonian deposits of 

 western Venezuela possess Mediterranean character (see Gerhardt, N. Jahrb. 

 Miner., etc., Bed., B. 1 1, 1897), but this is possibly explained by the assumption 

 that they formed part of the Caribbean Sea just formed (see above, p. 343). The 

 Mediterranean character of the Lower Cretaceous of Colombia, Ecuador and 

 Peru is easily explained by the Orinoco strait. 



