DALL: MOLLUSCA AND BRACHIOPODA. 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, and 
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 
Autillean 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 populous, 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 southern extreme of South America, 
where a few species extend northward on both shores of the continent, 
