ON MOLLUSCA OF THE WEST COAST OF NORTH AMERICA, 681 
American waters, which have bequeathed some species now flourishing, and 
others dying-out, to the existing seas. The present faunas of West America 
are perhaps the most isolated on the surface of the globe; yet, if we knew 
the ancestry of each specific form, we might find some first appearing with man 
on this planet, others first living even in historic times, others tracing their 
descent from remote periods, and it may be very distant localities, in the ages 
of the Miocene, possibly even of the Eocene oceans. These suppositions are 
not set forth as theories, but simply to guard against interpretations of facts 
based on conclusions which may be only the results of our necessarily 
imperfect information. 
123. With regard to forms offering local peculiarities sufficient to dis- 
tinguish them from correlative forms offering equal peculiarities in some other 
fauna, we are by no means warranted in assuming that these have sprung 
from different creations. Ifa race of men, migrating to a new continent, in 
a very few generations, or even in the next, develope an essentially different 
physique, it is fair to conclude that molluscs, borne by a change of currents to 
a distant region, or steadily migrating to the extreme limit of their con- 
_ ditions of life, will also change their appearance. If the publication of the 
“ Darwinian Theory” has had no other effect, it has at least checked the pro- 
pensity to announce ‘“‘new species” for differences which may fairly be re- 
garded as varietal. It must also be borne in mind, that if the views of Mr. 
Darwin be only a theory, such also is the name required for the prevalent 
opinion of separate creations for all diverse forms. What indeed can we 
possibly know of the mode of original creation of a single species? We can 
only prove that one or the other supposition best explains a certain class of 
facts. It is not necessary for a working naturalist to commit himself to an 
exclusive belief in either of these theories. He may perhaps best explain 
some facts by the doctrine of separate creation, others by that of natural 
selection. In either case it is his duty to trace-out, as far as possible, the 
limits as well as the powers of variation in every living form, and to guard 
against seeing that only which accords with his prevailing belief. 
124. The study of European shells, as they exist in Norway, in Britain, in 
the Mediterranean, at the Canaries, or as they appear at different depths 
and stations in our own seas, still more as they occur in the widely separated 
periods of the later and middle tertiary ages, is an excellent preparation for 
the examination of either recent or fossil faunas in districts where our know- 
ledge is fragmentary and unconfirmed. It may be safely stated that there are, 
in the American waters, many tropical forms from the West Indies and the 
Pacific shores, some temperate forms from California and the Atlantic, and 
many sub-boreal species in the Vancouver district and the European seas, 
not differing from each other more or even so much as forms universally 
allowed by malacologists to have had a common origin from Britain and the 
Mediterranean, from the Red and the Coralline Crag. 
125. It is interesting to observe that, notwithstanding the probable con- 
nexion of the oceans through the Rocky Mountains during the Miocene age, 
there is extremely little similarity between the special temperate faunas of 
East and West America. Not a single species has yet been proved identical, 
and the allied forms are but few in number. They appear as follows :— 
Californian species. U. S. Atlantic species, 
Clidiophora punctata, C. trilineata (? =nasuta), 
Lyonsia Californica. L. (hyalina= )Floridana. 
Macoma inconspicua. M. fusca. 
Angulus modestus. A. tener. 
Raéta undulata. R, canaliculata, 
