FROM THE MEDITERRANEAN AT JAFFA. 199 



enormous range of the marine species inhabiting the eastern hemi- 

 sphere. The majority of the shells of the Red Sea are found also in the 

 Pacific. 



Many shells which are found on Samoa and Tahiti occur at 'Akabah. 

 This at first seems strange when we consider the almost complete differ- 

 ence which exists between the fauna of the opposite coasts of the Atlantic, 

 but the above consideration explains it to a certain extent. 



The extreme dissimilarity between the faunas of the Red Sea and the 

 Mediterranean has been a subject of careful consideration by Issel in the 

 first part of his work already quoted. He finds eighteen species of mol- 

 luscs common to both seas, and thirty which are equivalent to each other, 

 or may be regarded as recent deviations from a parent stock. From a 

 comparison of the fossilized raised beach deposits of either seas he finds 

 that these seas were united in the Pliocene and Miocene times, and con- 

 tained a common fauna. If we accept this conclusion, which is probably 

 correct, we may view this ancient fauna as much more nearly related to 

 that now existing in the Pacific than that in the Mediterranean ; 

 decreased temperature during glacial times and since has rendered the 

 latter sea unfit for Pacific, warm-sea animals, which have, in the main, 

 long become extinct there. 



At the same time, the hardier Atlantic forms will have continually 

 pressed eastwards, and exterminated the lingering pre-glacial types. A 

 later union of post-glacial or glacial times between the two seas is believed 

 to have taken place, but this was, no doubt, of a shallow nature over a 

 wide sandy flat, and insufficient for any considerable interchange of life. 

 Those few common species (to which I have several to add) may not 

 unlikely date their advent to the Mediterranean from this most recent 

 geological period. And no doubt the Suez Canal is even now assisting 

 in this process. Some of my additions (Hyatea, lanthina) are of a 

 nature which would enable them readily to pass from one sea to the other 

 by this existing means. 



My list contains the following species known to exist in the Mediter- 

 ranean, but not before taken in the Red Sea : 



Hyalcea uncinnata, Brug. 



Cassis saburon, Lamk. 



lanthina nitens, Meuke. 



