414 CHARLES DARWIN 



this archipelago: a single fresh-water shell (Paludina) is 

 common to Tahiti and Van Diemen's Land. Mr. Cuming, 

 before our voyage, procured here ninety species of sea-shells, 

 and this does not include several species not yet specifically 

 examined, of Trochus, Turbo, Monodonta, and Nassa. He 

 has been kind enough to give me the following interesting 

 results: Of the ninety shells, no less than forty-seven are 

 unknown elsewhere a wonderful fact, considering how 

 widely distributed sea-shells generally are. Of the forty- 

 three shells found in other parts of the world, twenty-five 

 inhabit the western coast of America, and of these eight are 

 distinguishable as varieties; the remaining eighteen (includ- 

 ing one variety) were found by Mr. Cuming in the Low 

 Archipelago, and some of them also at the Philippines. This 

 fact of shells from islands in the central parts of the Pacific 

 occurring here, deserves notice, for not one single sea-shell is 

 known to be common to the islands of that ocean and to the 

 west coast of America. The space of open sea running north 

 and south off the west coast, separates two quite distinct 

 conchological provinces; but at the Galapagos Archipelago 

 we have a halting-place, where many new forms have been 

 created, and whither these two great conchological provinces 

 have each sent up several colonists. The American province 

 has also sent here representative species ; for there is a Gala- 

 pageian species of Monoceros, a genus only found on the 

 west coast of America; and there are Galapageian species 

 of Fissurella and Cancellaria, genera common on the west 

 coast, but not found (as I am informed by Mr. Cuming) in 

 the central islands of the Pacific. On the other hand, there 

 are Galapageian species of Oniscia and Stylifer, genera com- 

 mon to the West Indies and to the Chinese and Indian seas, 

 but not found either on the west coast of America or in the 

 central Pacific. I may here add, that after the comparison 

 by Messrs. Cuming and Hinds of about 2000 shells from 

 the eastern and western coasts of America, only one single 

 shell was found in common, namely, the Purpura patula, 

 which inhabits the West Indies, the coast of Panama, 

 and the Galapagos. We have, therefore, in this quarter 

 of the world, three great conchological sea-provinces, quite 

 distinct, though surprisingly near each other, being sepa- 



