OCR Text |
Show 1879.] ' L I G H T N I N G ' A N D 'PORCUPINE'EXPEDITIONS. 587 same kind, and which had been also considered extinct (viz. Leda or Tindaria solida, Seg., Nucula glabra, Ph., and Malletia dilatata,¥h.), 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 comparatively shallow water exists outside the Strait of Gibraltar, between Capes Spartel and Trafalgar. It is improbable that deep-sea Mollusca, 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 perhaps a succession of them, since the Pliocene period. For instance, the average depth at which Malletia excisa has been now found living is 1507-j 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 m y 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. ANOMIIDJE ANOMIA 2 II. OSTREID.E OSTREA 2 III. SPONDYLIDJE SPONDYLUS 1 IV. PECTINIDJE PECTEN 18 AMUSSIUM 3 LIMA 7 V. AVICULIDJE AVICULA 1 PINNA 1 VI. MYTILID.E MYTILUS 7 MODIOLARIA .... 4 CRENELLA 1 DACRYDIUM .... 1 IDAS 1 VII. ARCIDJE ARCA 10 GLOMUS 1 SILICULA 1 LEDA 22 NUCULA 10 PECTUNCULUS .... 2 LIMOPSIS 3 MALLETIA 3 Total........ 101 |