268 Isthmus Barriers Separating Fish Faunas 



that ordinary marine fishes or fishes of rock bottoms or of 

 deep waters did not cross it. 



3. It formed an open water to brackish-water fishes only. 



4. The types common to Japan and the Mediterranean did 

 not enter either region from the other by way of the Red Sea. 



5. As most of these are found also in India or Australia or 

 both, their dispersion was probably around the south coast of 

 Africa or by the Cape of Good Hope. 



6. In view of the fact that numerous East Indian genera, as 

 Zandus, Enoplosus, Toxotes, Ephippus, Platax, Teuthis, Acan- 

 thurus (Monoceros), Myripristis occur in the Eocene rocks of 

 Tuscany, Syria, and Switzerland, we may well suppose that an open 

 waterway across Africa then existed. Perhaps these forms were 

 destroyed in European waters by a wave of glacial cold, per- 

 haps after the Miocene. As our knowledge of the Miocene fish 

 faunae of Europe is still imperfect, we cannot locate accurately 

 the period of their disappearance. About half the species found 

 in the Eocene of Italy belong to existing genera, and these 

 genera are almost all now represented in the Indian fauna, and 

 those named above with others are confined to it. 



The study of fishes alone furnishes no adequate basis for 

 mapping the continental masses of Tertiary times. The known 

 facts in regard to their distribution agree fairly with the pro- 

 visional maps lately published by Dr. Ortmann (Bull. Philos. 

 Soc., XLI). In the Eocene map (Fig. 179) the Mediterranean 

 extends to the northward of Arabia, across to the mouth of 

 the Ganges. This extension would account for the tropical, 

 Eocene, and Miocene fish fauna of Southern Europe. 



The Cape of Good Hope as a Barrier to Fishes. The fishes 

 of the Cape of Good Hope are not well enough known for close 

 comparison with those of other regions. Enough is known of 

 the Cape fauna to show its general relation to those of India 

 and Australia. The Cape of Good Hope lies in the South Tem- 

 perate Zone. It offers no absolutely impassable barrier to the 

 tropical fishes from either side. It bears a closer relation to 

 either the Red Sea or the Mediterranean than they bear to 

 each other. It is, therefore, reasonable to conclude that the 

 transfer of tropical shore fishes of the Old World between the 

 Atlantic and Pacific, in recent times, has taken place mainly 



