IV. GEOGRAPHICAL DISTRIBUTION. 



Though the details of the distribution have already been given under each species, it 

 is desirable that a few lines should be devoted to a consideration of (l) the distribution of 

 the genus, and of the relations of the species, so far as regards their distribution, to each 

 other ; and (2) the factors that have caused, or at least aided, in bringing about the 

 distribution. 



HALOBATES. 



Wiillerstorffi is the most widely diffused species. It is pre-eminently the species of the 

 North Atlantic, and occurs also in the South Atlantic, Indian, and West Pacific Oceans. 



Micans is reported from the Atlantic, Indian, and Pacific Oceans, but seems to be very 

 rare, and it is possible that some confusion exists in the records, and that wiillerstorffi has 

 in some cases been confounded with micans. 



Sericeus is a species that seems very abundantly represented by individuals, but it is 

 almost confined to the Pacific, especially the North Pacific, of which it is pre-eminently 

 the species. It has been recorded as occurring near the Cape and near Madagascar, but 

 this is possibly an error of determination. I have before me two specimens (from the 

 Challenger) from the North Atlantic. I cannot think that there is a mistake about 

 the locality of these, but still, corroboration is very desirable. 



Flaviventris is a rare species. I have seen specimens from near St. Helena, and from 

 near Ceylon, and it has also been reported from near Madagascar. 



All the remaining species are, so far as we yet know, very limited in their distribution. 



Streatfieldanus has only once been taken in the South Atlantic ; hayanus occurs at 

 Aden ; frcmenfeldanus at the Nicobars ; proavus near Gilolo ; jyrinceps in the Celebes Sea ; 

 and germanus and sobrinus in one or two localities in the Pacific. 



To sum up, five species' occur in the Atlantic, but one only is (so far as we know) 

 restricted to that ocean, though the headquarters of another appear to be there. 



Six species, of which two are peculiar, occur in the Indian Ocean, west of long. 100° E., 

 while to the east of long. 100° E., and chiefly in the West Pacific, eight species occur, of 

 which four are restricted to that region. But if we take the Indian Ocean and West 

 Pacific together, we find that nine out of the eleven known species occur there, and five 

 nowhere else. It would seem, therefore, that the region between the eastern part of the 

 Indian Ocean and the West Pacific is the metropolis of the genus, and it does not seem to 



