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The collection of Arctic Hydroids formed by Dr.
Stux-berg, the zoologist accompanying Baron Nordenskiöld
on his great circumnavigation in the Vega, contains no
verv conspicuously new or remarkable forms, although much
of it was got in seas never searched by naturalist before.
Yet it is not without interest, for it extends greatly the
known area of distribution of many forms, and contains
spe-cimens of several difficult and little-known species. And it
links together the comparatively well-known Hydroid faunas
of Barents. Sea and the N. Atlantic on the one hand, and of
Bering Strait and Alaska on the other.
The general similarity between these two faunas is very
great. The same genera are characteristic of both, and the
same types of species; though absolute specific identity is
comparatively rare at the two extremes.
Obelia longissima, Gonothyrcea hyalina, FileUum serpens,
La-foea fruticosa, probably Sertnlarélla gigantea, Sertularella
tricuspi-clata, appear at both limits, the last species only showing slight
characteristic differences.
Sertularia abietina at the eastern limit seems to be
repre-sented by S. variabilis at the western; Thuiaria articulata by
T. turgida. While the limited group of Thuiarians to which
the so-called Sertularia cupressina and argentea belong, is
characteristic of the whole area, these species being replaced
towards the west by T. Vegce, n. sp., T. plumosa, and T.
robusta. 1
In many cases our eollections show no such transition.
Our common N. Atlantic Campanularia verticillata is exceedingly
like Clarke’s Alaskan C. circula: and nevertheless the Vega
collection only brings the former species from an extreme N. W.
European station, and has neither of these nor any similar
form from intermediate points.
1 Also T. (S.) similis, T. cupressoides, and S. thuiaroides, closely allied
Alaskan species described by Clarke but not represented in the Vega
collection.
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