324 M. C. Mereschkowsky on the Hydroida. 
34. 8. abietina, Linn. 
35. S. argentea, Ellis & Sol. 
36. S. albimaris, nov. sp. 
37. Hydrallmania falcata, Linn., var. bidens. 
38. Thutaria thuja. 
39. T. articulata (?). 
40. Polyserias mirabilis, Verrill. 
41. P. Hinckswi, nov. gen. et nov. sp. 
Suborder GYMNOCHROA. 
42. Hydra oligactis, in the fresh water of the isle of Solo- 
vetzky. 
It will be seen that among the forty-two species there are 
about eight which are new; the Hydroid fauna of the White 
Sea is therefore a rather peculiar one. Besides this we also 
see that as regards its fauna the White Sea belongs to regions 
which are quite polar, more polar, in fact, than the north of 
Norway and even the Mourmansky bereg (north of Lapland). 
Thus, while the White Sea has no representative of the family 
Plumulariide, which is characteristic of the southern seas, 
and, on the other hand, has many representatives of the fami- 
lies Lafoéide, Coppiniide, and Sertulariide, the Mourmansky 
bereg has furnished magnificent specimens of Antennularia 
antennina, of which the Zoological Cabinet of St. Petersburg 
is in possession. The Baltic has several species in common 
with the White Sea; but all these species are represented in 
England, Germany, or Belgium ; they have consequently been 
able to arrive there through the Cattegat and Skagerrack, 
without its being necessary to explain this fact by the assump- 
tion of a union between the two seas; so that, as far as the 
Hydroids are concerned, they do not present any’ facts in 
support of Lovén’s hypothesis, which, moreover, has been 
much shaken by the investigations of Prof. O, Grimm, of 
St. Petersburg*. Lastly, on comparing this fauna with that 
of the north of the Pacific Ocean, as represented by Mr. Clark, 
and also by the collection of the Museum of the Academy of 
St. Petersburg, it will be seen that there are relations between 
these two faunas. The genus Polyserias is especially charac- 
teristic of the north of the Pacific (I am acquainted with three 
species of this genus from the sea of Ochotsk) ; and, as we see, 
the White Sea possesses two species, one of which is common 
(Polyserias mirabilis). Further, the presence of Coppinia 
arcta, Lafoéa dumosa, Campanularia integra, Lafoéa pocillum, 
* O. Grimm, ‘On the Fauna of the Baltic Sea and its Origin’ (in 
Russian), 1877. 
