DALL: MOLLUSCA and BlUCHIOPODA. 207 



also true that many others, sometimes associated with the former, so far 

 as yet known have a quite restricted range. The reference of any par- 

 ticular species to the one or the other of these groups will therefore 

 necessarily depend upon actual observation. 



The material obtained northwest from Panama is less abundant than 

 that from the Gulf of Panama, the vicinity of the Galapagos Islands, ami 

 of the southwest coast of the Chilian territory, formerly referred to as 

 western Patagonia. Hence the lists may be regarded as more complete 

 for the west coast of South America than for the deeps further north. 

 There are in the text a considerable number of species discussed which 

 do not appear in the lists, having been collected by the " Albatross " party 

 from moderate depths of water or even on the shores between tides. As 

 a whole, however, this report will add materially to our knowledge of 

 the West American fauna of both deep and shallow water. 



The opportunity seems good for making some comparisons between 

 the deep-sea fauna of the West American region we are considering and the 

 fauna disclosed by the researches of the " Blake," " Hassler," and other 

 expeditions on the Atlantic side of the continent, and especially in the 

 Antillean region. The latter was fully reviewed in my report on the 

 " Blake " Mollusca, and the data are therefore ready for making the com- 

 parison, which will leave out of consideration the forms belonging to the 

 shallows. If the comparison was made without this discrimination, many 

 of the most striking features of it would be lost. It seems probable that 

 the fauna of the deeps is very ancient, while that of the shallows may 

 date from the late Pleistocene in some cases. Therefore, assuming that 

 the deep-sea fauna is reasonably well known, the contrast between the 

 faunas of the adjacent portions of the two oceans should be suggestive 

 and important in connection with geological theories as to the former 

 relations of seas and shore lines. 



The known fauna of the eastern Pacific deep sea, as previously limited, 

 contains about 300 species of Mollusks, if we omit pelagic species which 

 only appear on the bottom, after death, like the Pteropods, Janthina, 

 the Argonauts, etc. These are really inhabitants of the superficial strata 

 of the sea and have no place in this discussion. These 300 species are 

 divided into 134 generic and subgeneric groups, but some groups are 

 very popidous, while the larger number are represented by but one or 

 two species. The Antillean region possesses 174 groups and a much 

 larger number of species. There are practically no species common to 

 the two regions, except at the smithern extreme of South America, 

 where a few species extend northward on both shores of the continent, 



