208 BULLETIN: MUSEUM OF COMPAEATIVE ZOOLOGY. 



but do not reach the Antillean or Panamic regions. A few species like 

 Bathyarca corpulenta, or some of the Solemyas, have a very wide range 

 oyer the floor of the Pacific Ocean. Among brachiopods Discinisca 

 aflanfica is common to the two oceans, and in the Atlantic to both 

 hemispheres. The presence of the Terehratulina crossei in both Japan 

 and Patagonia, to my mind, requires confirmation. I have seen nu- 

 merous specimens from Japan, but nothing of the kind from the Magel- 

 lanic region, and this is not an abyssal species, like Terehratula 

 moseleyi. 



That a certain proportion of the North Pacific fauna of the deep sea 

 originated in the south seems highly probable. The north, however, 

 seems also to have contributed its migrants. When the question of 

 " bipolarity " is raised, and based upon a few supposedly identical 

 species, it is but feebly, if at all, supported. But if generic and sub- 

 generic groups be taken instead of species for comparison, an undeniable 

 " bipolarity " is displayed. But this question is one with which our 

 present faunal area is only distantly connected. 



Our fauna, which I shall for brevity in this discussion call the " Pa- 

 cific" fauna, contains about 300 species, belonging to sixty-seven families. 

 Of these eight families furnish more than half, and three of these family 

 groups contain one-third of the whole fauna. 



Turritidae contains 57 species 



Lediilae " 35 " 



Dentaliidae " 14 " 



Pectinidae " 13 " 



Nuculidae and Naticidae, each 11 " 



Trochidae and Limopsidae, each 9 " 



The total number of species in these eight families is 159, leaving 141 

 species for the other fifty-nine families, or little more than two species 

 apiece. 



The Antillean fauna has 174 distinct generic and subgeneric or sec- 

 tional groups of importance represented. The Pacific fauna has only 

 144. But of all these groups only eighty-nine of mollusks are common 

 to both faunas and six of brachiopods. 



The Pacific has three groups of bracliiopods and twouty-seven of nml- 

 lusks not represented in the Antillean fauna. 



Tho Antillean ha.s three groups of brachiopods and seventy-six of mol- 

 lusks not represented on tlie Pacific side. 



These statistics would indicate, if confirmed by further researches, 



