6 BULLETIN 112, UNITED STATES NATIONAL MUSEUM. 



A few Mediterranean forms such as Gibbula adriatica and C'yma- 

 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, Harpa, and Cymia, but are well repre- 

 sented by living forms in the Pacific. Again note the profusion of 

 Haliotis 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 numerous species because it 

 familiarizes the student with the subdivisions Avhich 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 where 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- 



