HYDROIDS OF THE HAWAIIAN ISLANDS. 
935 
An analysis of the foregoing table shows that of the 51 species included 31 are 
peculiar to the Hawaiian region, leaving 20 that are found elsewhere. Of these 
latter 7 may be regarded as Holaretic, all being found in the arctic region and on the 
coasts of northern Europe, as well as in the North Pacific; these are Eudendrium 
rameum , Eudendrium capillars , Calycella syringa , Filellum serpens, hdfoea durnosa, 
Lafoea fruticosa and Lictorella lialecioides. All but one of these (. Eudendrium 
rameum) have been found on our New England coast and 4 of them have been 
reported from Alaska. 
Excluding these Holaretic forms and Pasythea quadridentata , found in temperate 
and tropical seas throughout the world, there are 12 species still to be discussed. 
Seven of these — namely, Ceratella fusca , Campanularia spinulosa, Sertularella lata, 
Thuiaria fenestrata, Synthecium orthogonia , Plumularia buskii, and Lytocarpus 
phceniceus — are, with a single exception**, known to occur only in the Australian 
region. Of the remaining 5 species 2, Sertularia dentifera and Plumularia corru- 
gata , have hitherto been reported from the California coast onty; and 3, Synthe- 
cium tubithecum , Monostsedias quadridens, and Aglaophenia rigida, are West Indian, 
although the last of these is identified with much doubt. 
Recapitulating, the distribution of the known Hawaiian species of hydroids may 
be summed up as follows: 
Species peculiar to the Hawaiian region 31 
Holaretic species 7 
Pelagic and widely distributed 1 
Australian species 7 
Californian species 2 
West Indian species 3 
As would be expected from the isolated position of the Hawaiian Islands, the 
preponderance of peculiar species is very exceptionally large. At first sight it would 
appear that the Holaretic and Australian relationships were equal. A little consid- 
eration, however, will show us that the relationship with Australia is decidedly more 
intimate than that with the more northern great faunal area. This- is strikingly 
shown, as has already been intimated, by the large number of plumularians included 
in the collection, embracing about one-third of the entire series. The occurrence of 
Ceratella fusca, a representative of an essentially Australian famity, is also significant. 
In connection with the appearance of three West Indian forms in the Hawaiian 
Islands it is interesting to remember that Dr. Alexander Agassiz, in discussing the 
echinid fauna of the West Indies, says: 
The resemblance of the fauna of the Gulf of Mexico and the Caribbean to that of the Pacific was 
noticed by writers, even at a time when the materials available for comparison included but little 
beyond the littoral fauna. * * * In fact, the deep-sea fauna of the Caribbean and of the Gulf of 
Mexico is far more closely related to that of the Pacific than to that of the Atlantic. Before the 
Cretaceous period the Gulf of Mexico and the Caribbean were undoubtedly in freer communication with 
the Pacific than with the Atlantic Ocean. & 
It is somewhat strange that the large and cosmopolitan genus Sertularia has but 
one representative in the collection. This seems all the more remarkable when we 
« Sertularella lata was secured by the Challenger on the Brazilian coast. 
{"Three Cruises of the Blake, vol. i, p. 157, 1888. 
