396 On the Molluscan Fauna of the OuJf of 8uez. 



the minimum being 62°, the maximum 80° ; the same at 

 Suez is 74°-75° F., minimum 68°, maximum 80°. This, it 

 must be remembered, is the surface-temperature, and any 

 difference therein exhibited would have a tendency to diminish 

 when the water at several fathoms' depth was examined. It 

 does not appear that the amount of salt contained in the sea- 

 water at these places has ever been definitely compared by 

 experiment ; but, judging from what one can learn of the 

 water at Suez *, and of the average saltness of the Mediter- 

 ranean t, there does not appear to be any large difference 

 between them. 



That se])aration from the parent stock will in the end 

 prevail, and that these Red- Sea shells will gradually become 

 more and more unlike their Mediterranean ancestors, is not 

 denied. Differences, however slight, ™^y ii^ the end esta- 

 blish themselves, though it be quite possible that the Suez 

 Canal may do something towards the equalization of the 

 character of the water of the two seas as well as in intro- 

 ducing fresh batches of the parent stock. It seems no unreason- 

 able assumption that species which were the first to migrate 

 in Postpliocene times will be the first to migrate now ; at 

 any rate, they are at least as likely to migrate as any others. 

 At the same time I fully anticipate that, as the lied Sea 

 becomes better explored, forms will be discovered which will 

 connect species hitherto regarded as distinct, and thus the list 

 that I have here presented will become gradually increased. 



It only remains to mention in this last connexion a very 

 interesting and remarkable paper by Dr. Conrad Heller J, 

 which shows that the opening of the Suez Canal has, appa- 

 rently, already induced several species of Mollusca to start on 

 their travels, not only from the Mediterranean to the Red Sea, 

 but in the reverse direction as well. Indeed, while at least 

 two undoubted Red-Sea species {Mactra olorina, Phil., and 

 Mytilus variahilis, Krauss) had, in 1882, established them- 

 selves at Port Said, only one Mediterranean species [Gardiimi 

 edule^ L.) had reached even the large Bitter Lakes, and it 

 might possibly have been living there before, as C. isthmicum, 



• The sea-water at Suez contains a veiy small fraction over 4 per cent, 

 of saline matter. Maury, ' I'liys. Geogr. of the Sea/ p. 190 ; Trans. Bomb. 

 Geogr. Soc. vol. ix. 1849-50. 



t " Recent experiments have shown that the water of the Mediter- 

 ranean contains full 4 per cent, of salt. M. Bouillon la Grange investi- 

 gated the subject witli great perseverance, and his conclusion is, assuming 

 the proportion of saline matter in the water of the Atlantic Ocean to be 

 38, that of the Euglish Channel will be 36, and that of the Mediterranean 

 41." — Smyth, ^Mediterranean,' p. 127. 



\ " Die Fauna im Suez-Canal und die Diffusion der mediterraneen und 

 erythraischeu Thierwelt." Dated Zurich, Sept. 1882. 



