CHAP. XIII MEDITERRANEAN AND RED SEA FAUNAS 251 



As Dr. Gunther says, " The system of the Jordan presents 

 so many African t}'pes that it has to be included in a descrip- 

 tion of the African region." ^ He adds, moreover, that " this 

 infusion of African forms cannot be accounted for by any 

 accidental means of dispersal," and thus it appears to afford 

 conclusive proof of an original connection between the rivers 

 of Palestine and Central Africa. 



At first it seems to be very easy to account for this con- 

 nection, by assuming that a river from the Jordan basin was a 

 tributary of the Nile, at the time when the eastern end of the 

 Mediterranean was dry land. We know that the Levant was 

 land in Pliocene times, for thus only is it possible to account 

 for the almost complete difference in the faunas of the two seas 

 on either side of the narrow isthmus of Suez. This difference 

 is perhaps the most impressive fact in the whole range of 

 zoological distribution. Thus in the case of the Sea-Urchins, 

 not one species was common to the two seas at the opening of 

 the Suez Canal. The evidence of the Mollusca is equally con- 

 clusive, for according to Mr. Edgar Smith,' who has issued the 

 last authoritative statement on the subject, only eight species live 

 on both shores of the isthmus. This number is quite insig- 

 nificant in proportion to the enormous faunas of the two seas, 

 while the presence of the eight species in both seas can be 

 easily explained. A couple of them {Chiton siculus, Gray, and 

 C. discrepans, Br.) live attached to seaweeds, and could easily 

 have been blown across the narrow isthmus ; the other six 

 occur also in the Atlantic, and could thus have reached the 

 Mediterranean through the Straits of Gibraltar. The evidence 

 of the Mollusca is therefore as conclusive as that of the Sea- 

 Urchins, in disproving any recent connection between the Medi- 

 terranean and the Red Sea. But the separation between the 

 two seas cannot have been always effected by the present isthmus 

 of Suez ; for the geological evidence shows that the Red Sea 

 extended farther north in Pleistocene times, and then actually 

 occupied part of the present site of the Mediterranean. It 

 is now generally believed that the passage of the Red Sea 

 by the Children of Israel must have been effected at some 



1 A. Giinther, The Study of Fishes, 1880, p. 227. 



^ E. A. Smith, "On a Collection of Marine Shells from Aden," Proc. Zool. Soc. 

 (1891), p. 398. 



