680 REPORT—1863. 
Terebratula nitens, Cony., is very probably Waldheimia pulvinata, Gd. 
Bulla petrosa, Cony., has the shape of Tornatina eximia, Bd. 
Crepidula prorupta, Cony., is certainly princeps, Midd. 
Turritella, sp. ind., resembles Mesalia lacteola. 
? Dolium petrosum, Conr., resembles the young of Priene nodosa, Chemn. 
Fusus geniculus, Conr, A similar shell has just been taken at the Farallones 
by Dr. Cooper. 
121. To correct the general table of “ Mollusca of the West Coast of N. 
America” (First Report, pp. 298-345), and the deductions founded upon it 
(pp. 346-367), would involve the necessity of reprinting a considerable por- 
tion. The student, being now in possession of all the known sources of 
fresh information, can with his own pen strike out the spurious species, alter 
the synonyms, insert the newly discovered forms, and make the requisite 
corrections in the classified results. 
122, With regard to the tropical fauna, the researches at Cape St. Lucas 
and in the interior of the Gulf of California, though leaving much to be 
desired, bear-out the general conclusions arrived-at in paragraphs 78-87. 
_The evidence for the identity of specific forms on the Atlantic and Pacific sides 
of Central America has been greatly confirmed. Dr. Gould writes, “The 
doctrine of local limitations meets with so few apparent exceptions that we 
‘admit it as an axiom in zoology that species strongly resembling each other, 
derived from widely diverse localities, especially if a continent intervenes, 
and if no known or plausible means of communication can be assigned, 
should be assumed as different until their identity can be proved (vide E. E. 
Moll. Intr. p. xi). Much study of living specimens must be made before 
the apparent exceptions can be brought under the rule.” It has, however, 
to be borne in mind that the researches of modern geology clearly point to 
considerable alterations in the existing configuration of continents, and in 
the consequent direction of ocean-currents, during the ascertained period of 
many species now living. Nor are we warranted in the belief that the 
existing fauna in any locality has been created at any one time, or has 
radiated from any single spot. To study the relations of living shells simply 
in connexion with the existing map of the world must lead but to partial 
results. The facts accumulating with regard to the British species, by 
tracing them through the northern drift (now found even on the Snowdonian 
range), to the oldest crag deposits when Europe was contained in far different 
boundaries, show how altered may have been the configuration of the new 
world when the oldest of its molluscs were first created. Coordinately with 
the glacial period, Central America may haye been a group of islands ; co- 
ordinately with the creation of Saxicava pholadis and Chrysodomus antiquus, 
the gulf-weed may have floated between the Rocky Mountains in the 
archipelago of West America, and Japanese molluscs may have known how 
to migrate to the Mediterranean shores. Dr. Gould’s position may there- 
fore be accepted in theory ; yet, in practice, the “ imperfection of the geological 
record” *, and even of our knowledge of existing species and their variations, 
demands that the greatest caution be exercised in building results on deduc- 
tions from our ignorance. Already the fossil Malea ringens of the Atlantic 
has proved a “ Rosetta Stone ” to interpret the Cyprea exanthema, Purpura 
patula, and other Caribbean shells of the Pacific ; and as the geology of the 
West Coast advances, so may we expect to find traces of previous denizens of 
* No student of geographical distribution should omit to weigh carefully the chapter 
on this subject in Darwin’s ‘ Origin of Species,’ and the information given in Lyell’s 
§ Antiquity of Man,’ 
