1879.] 'lightning' AND 'PORCUPINE* EXPEDITIONS. 587 



same kind, and which had been also considered extinct (viz. Leda or 

 Tindaria solida, Seg.,Nucirf a glabra, Ph., and Malletia dilatata, Ph.), 

 occurred in the • Challenger' Expedition. The communication between 

 the North Atlantic and the Mediterranean must have been formerly 

 very different from what it is now, when a barrier or ridge in compara- 

 tively shallow water exists outside the Strait of Gibraltar, between 

 Capes Spartel and Trafalgar. It is improbable that deep-sea Mol- 

 lusca, even in their embryonic state, could have migrated or been 

 transported under such conditions from one sea to another. The south 

 of France and Italy must have experienced a great elevation, and per- 

 haps a succession of them, since the Pliocene period. For instance, the 

 average depth at which Malletia excisa has been now found living 

 is 15073 fathoms, or 9044 feet, being very nearly five-sixths of the 

 height of Mount Etna above the present level of the sea ; and to 

 this submarine elevation must be added the height of the Pliocene 

 beds above the sea-level. Professor Seguenza informs me that 

 M. excisa occurs in Sicily, as well as in Calabria, at a height of 

 600 metres or nearly 2000 feet, and that these fossiliferous beds 

 attain double that height in other parts of the same district; so that 

 the total elevation may be estimated at from 11,000 to 12,000 feet. 

 Mount Etna is 10,874 feet high. 



I have to acknowledge my obligations to the Rev. R. Boog Watson 

 for his kind assistance in examining and comparing some of the 

 ' Challenger' shells above referred to. 



Summary of the foregoing Mollusca. 



Families. Genera. No. of species. 



I. ANOMIIL^E Anomia 2 



II. OSTREIL\E Ostrea .... 2 



HI. SPONDYLID^E Spondylus 1 



IV. PECTINHLE Pecten 18 



Amussium 3 



Lima 7 



V. AVICULID^l Ayicula 1 



Pinna 1 



VI. MYTILID^E Hytilus 7 



Modiolaria .... 4 



Crenella 1 



Dacrydium 1 



Idas 1 



VII. ARCID.E Arca 10 



Glomus 1 



Silicula 1 



Leda 22 



Nucula 10 



Pectunculus .... 2 



Limopsis 3 



Malletia 3 



Total 101 



