6 BULLETIN 112, UNITED STATES NATIONAL MUSEUM. 
A few Mediterranean forms such as Gibbula aclriatica and Gyrna- 
tium corrugatum appear in the Californian fauna, but no plausible 
explanation of their presence occurs to me. 
Certain discrepancies between the groups of mollusks both in deep 
and shallow water on the two sides of America were pointed out by 
me in the discussion of the data in my reports on the dredgings of 
the Blake and Albatross, For instance the profusion of species of 
the Marginellidae in West Indian waters and their scarcity on the 
Pacific side. Some genera are found only fossil on the Atlantic 
shores, such as Strombina,, Ilarpa,, and Cymia,^ but are well repre- 
sented by living forms in the Pacific. Again note the profusion of 
Tlaliotis on the shores of the Pacific with only a single depauperate 
deep water species in the western Atlantic. The great number of 
Pacific Tritonalia and other muricoid species contrasts strongly with 
their paucity on the opposite shores. The late Dr. Philip Carpenter 
used to lament the absence on the Atlantic coast of the myriads of 
minute Gastropods he was accustomed to collect on British hunting 
grounds. That the difference is real, is proved by the scanty rewards 
which have fallen to New England collectors. But no such scarcity 
would have been noted had Doctor Carpenter been a west coast 
collector. 
These singularities of distribution will doubtless find an explana- 
tion when the recent and fossil mollusk faunas of the two areas are 
more thoroughly known. At present, hypotheses must be regarded 
as premature. 
A few remarks on the classification adopted may be in order. Of 
late years some specialists on particular groups, having small knowl- 
edge of any but their own particular field, have naturally exaggerated 
the importance in a classificatory sense of certain features of the 
subjects of their studies. Two or three bristles in a particular place 
have sufficed to establish a dipteran genus. This sort of taxonomy 
does not appeal to me and I have, except in extremely populous 
groups where convenience requires more laxity, endeavored to exer- 
cise a reasonable conservatism in the adoption of divisional names 
of higher rank than species. I have preferred to utilize the sub- 
generic names in groups containing numercus species because it 
familiarizes the student with the subdivisions which in many cases 
will doubtless reach generic rank at some future time under more 
intensive study than is at present practicable. Also because of the 
greater convenience in handling populous groups. In the case of 
species and varieties, I have preferred inclusiveness to lumping in all 
cases v/here doubt existed, but I have not included names based upon 
mutational color patterns except when the differences are so marked 
as to be a possible source of misunderstanding to the inexperienced 
student. In many groups these differences are due to food, or pe- 
