Annual Report.] 194 [May 1, 



apparently identical species from widely different sources 

 rapidly diminishes. In fact the doctrine of the local limita- 

 tion of animals meets with so few exceptions, that we admit 

 it as an axiom in zoology, he says, that species resembling 

 one another from widely diverse localities, especially if a 

 continent intervenes, and if no plausible means of communi- 

 cation can be assigned, are different until their identity can 

 be proved. It is true that some species are more or less cos- 

 mopolite, as the Cypreas, and as at present understood, do 

 not appear to be limited by seas, while others become cos- 

 mopolite by transportation, as certain Helices, which r.ttach 

 themselves to the water-casks of ships, and thus are carried 

 around the world. 



Another general consideration, and closely related to geo- 

 graphical distribution, grows out of the fact that the shells 

 from definite regions have peculiarities of external form and 

 color, of what may be called style, just as have the human 

 races from different parts of the world. Thus, he says, we 

 distinguish the loose, colorless structure of the northern spe- 

 cies, the stony, corroded and livid New Zealanders, and the 

 jDohshed and absolutely perfect specimens from the coral seas. 



Another generalization illustrated by the amjile stores of 

 the Expedition, is the occurrence of analogous species in co- 

 ordinate regions, though the species themselves are absolutely 

 distinct ; in confirmation of which he gives a list of some 

 thirty-two species found on the eastern and western coasts 

 of the United States. 



Lastly, it is shown by a careful comparison cf the land 

 shells of the Pacific islands, how one is helped in drawing 

 inferences as to the lands which once occupied the area of 

 the Pacific, and how, in consequence of their submergence, 

 their mountain peaks, which noAV alone project above the 

 surface of the water, constitute these islands. The Samoa 

 and Friendly Islands give evidence of such relation in hav- 

 ing identical species. 



The Otia Conchologica was the last of his printed vol- 

 umes, but this was merely a reprint in a condensed form of 

 the descriptions of species of shells previously published sep- 

 arately in different works. Besides the works already men- 



