514 



THE AMEKH AS 



Vol. XLIII 



Miocene may be taken as the date of origin of the modern 

 genera of marine fishes, he contends that an open com- 

 munication between the two oceans may have existed 

 during that geological period. It is important to note 

 that the sea currents seem at that time to have set west- 

 ward, thus favoring the transfer of Atlantic rather than 

 Pacific types across the isthmian area. 



Mr. Regan 3 is inclined to put the date still a little 

 further back in urging that the marine connection between 

 the two oceans ceased to exist at the beginning of the 

 Mioeene. 



An investigation of the Crustacea and their distribu- 

 tion led Dr. Ortmann 4 to the conclusion that at the dawn 

 of the Tertiary era an oceanic connection was in actual 

 existence between the Atlantic and the Pacific in the 

 isthmian region. This communication, he thinks, per- 

 sisted until the Miocene. In the commencement of that 

 period the isthmus was elevated, thus joining North and 

 South America. 



The Mexican amphibians and reptiles have been uti- 

 lized by Dr. Gadow 5 in the solution of the same interest- 

 ing problem with the result that he assumes the establish- 

 ment of land-continuity between North and South America 

 in either late Oligocene or early Miocene times. 



The whole character of neotropical zoology, remarks 

 Dr. Wallace, 6 whether as regards its deficiencies or its 

 specialties, points to a long continuance of isolation of 

 South America from the rest of the world, with a very 

 few distant periods of union with the northern continent. 



Geologists have discussed this subject mostly from 

 paleontological evidence. Professor Gregory 7 clearly 

 demonstrated that the idea of an interoceanic connection 

 as late as the Pleistocene period, as suggested by T)r. 

 Spencer, 7a could no longer be entertained. In arriving 



3 Regan, C. T., "Fishes of Central America," p. xxx. 



4 Ortmann, A. E., "Geographical Distribution of Decapods," p. 359. 

 s Gadow, H., "Mexican Amphibians and Reptiles," p. 236. 

 'Wallace, A. R., "Distribution of Animals," Vol. II, p. 80. 

 'Gregory, J. W., "Paleontology of the West Indies," p. 305. 



