1902.] AND ANCIENT GEOGRAPHY. 359 



land mass to the south and west of the isthmus cannot have formed an 

 Old Tertiary barrier completely separating both oceans, since we 

 need an interoceanic communication during this time, as we shall 

 presently see. 



Our opinion is, that during the Cretaceous there was a connection 

 between northern Central America and northern South Atnerica, the 

 Antillean continent still being more or less intact. At the beginning 

 of the Tertiary, however, and after the forination of the Caribbean 

 Sea, an oceanic connection existed between the Atlantic and Pacific 

 in the isthmian region, and this communication existed up to the 

 Miocene, separating North and South America. But afterward, 

 beginning in the Miocene, the isthmus was elevated, reconnecting the 

 separated chief remnants of the Antillean continent, and at the same 

 time North and South America. The Atlantic and Pacific Oceans 

 were separated, and never again communicated, either here or else- 

 where} 



We here arrive at a result which differs considerably from von 

 Ihering's ideas as to the relations of North and South America: 

 von Ihering believes (1894, p. 405) that both continents were sepa- 

 rated by Cretaceous sea, and that Central America was entirely 

 submerged at this time ; the origin of the Isthmian land-bridge is 

 also placed by von Ihering in the Miocene. 



For our Crustaceans, we are to draw from this the following con- 

 clusions : 



The presence of Potamocarciuince in the present continental parts 

 of the old Antillean continent, in Nicaragua, Guatemala (to which 

 we must add the southern parts of Mexico), the isthmian region and 

 Venezuela, is due to the Cretaceous connection of these parts ; the 

 presence of the genus Epilobocera in the Greater Antilles is due to 

 the former connection of these islands with the mainland, and 

 belongs to the same land period, or to the continuation of it in the 

 earlier part of the Tertiary. After the separation of the Greater 



1 This idea well agrees with the character of the present Atlantic and Pacific 

 marine littoral faunas in the Central American region. These faunistic facts are 

 often incorrectly represented and understood, and Hill's argument against the 

 importance of the interoceanic communication in older Tertiary times is based 

 upon such a misunderstanding. I have studied this question chiefly with refer- 

 ence to the marine Decapod Crustaceans, and shall give below a correct repre- 

 sentation of the actual conditions of the faunal relations of both oceans. See 

 Appendix. 



