MoUuscan Fauna of the Gulf of Suez. 387 



way become impregnated with a very strong Mediterranean 

 leaven. 



The opposite pole of belief is occupied by M. Fischer. 

 That distinguished writer, in an article * on the shells col- 

 lected by M. Vaillant at Suez (in which, however, only 86 

 species in all are enumerated) , concludes that " il n'existe 

 aucune coquille commune a la mer Rouge et a la Mdditer- 

 ran^e." In a later article f M. Fischer, reasoning on the 

 analogy of closely allied species occurring on both sides of 

 the Isthmus of Panama, suggests a common derivation for 

 closely allied species in the lied Sea and Mediterranean, such 

 derivation to date from the Miocene period, after which he 

 supposes the isthmus to have been finally closed. 



Unfortunately M. Fischer had not sufficient material to 

 support his theory, which indeed he rested entirely on the 

 occurrence of Cardium edule (fossil) at Suez and (recent) 

 along the isthmus, and on the erroneous idea that Nassa 

 gihhosula, Gmel., was common to both seas. 



This theory, however, which is in its main point thoroughly 

 scientific, and which only failed in M. Fischer's hands from 

 want of material, was adopted and established by Sign. Issel. 

 That author, in the preface to his ' Malacologia del Mar 

 Bosso,' after referring to Fischer's assertion of the entire 

 difference between the two faunas, makes some remarkable 

 observations, which are worth translating : — 



" Though it would be incorrect to assert that there does 

 not exist one single species common to the Mediterranean and 

 the Red Sea (species being understood in the sense commonly 

 accepted by conchologists), yet it is none the less true that 

 there do not exist in the two seas two identical shells. The 

 fact is, Mediterranean species which have been brought from 

 the Red Sea all differ more or less from their respective typical 

 forms. Nassa costulata of the Red Sea is more elongated and 

 smaller ; Solecurtus strigilatuSj while remaining constant in 

 form, shows on its valves closer and more numerous striae j 

 Oastrochcena duhia is more deeply striated than Mediterranean 

 specimens. 



" It might be objected that these forms, being so decidedly 

 different, ought therefore to constitute distinct species, and 

 therefore the assertion formulated by M. Fischer would be 

 perfectly correct. 



" To this we would answer that the distinctive characters 

 observed by us in some Red-Sea varieties are not sufficient to 

 characterize separate and distinct species (species being under- 



* ' Journal de Conchyliologie,' 1865, pp. t»7-127, 241 248. 

 t lb. lb7U, pp. lUl-179 ; 1871, pp. 209-920. 



