220 M. C. Mereschkowsky on 7iew Species 



on certain portions of the shoots, as rather short and stout 

 processes, which give otf towards the free extremity a number 

 of tendril-like claspers, by means of which, Ave may suppose, 

 the slender tufts cling to some neighbouring support. They 

 are also present in the more usual form of simple tubes, and in 

 this condition form a dense and tangled mass of rootlets at 

 the base of the shoots. 



We know that some foreign species are also furnished with 

 hooked fibres such as we find on Scrupocellarm reptans ; and 

 in all such cases we have, no doubt, a similar adaptive modifi- 

 cation of the simpler structure. 



XXX. — On a new Genus of Hydroids from the White Sea, 

 loitk a short Description of other new Hydroids. By C. 

 Mereschkowsky. 



[Plates V. & VI.] 



During the summer of 1876 I undertook a journey to the 

 White ISea, the zoology and botany of which are almost com- 

 pletely unknown, with the object of studying its fauna as 

 thoroughly as possible, my attention being principally de- 

 voted to the study of invertebrated marine animals. My ex- 

 pectations were fully realized ; for this sea, hitherto completely 

 unexplored and almost entirely separated from the Arctic 

 Ocean, afforded me numerous and highly interesting speci- 

 mens of types differing from those generally observed. 



Amongst these I may mention a new and interesting 

 Hydroid, which I now propose to describe. 



Ln the part of the White Sea called the Bay of Onega, at 

 small depths (5 fathoms), and where the bottom is slimy, 

 specimens of Tellina solidida are frequently found, with the 

 edge of the shell covered with an agglomeration of small 

 animals of a light yellowish colour, giving off long, thin, 

 floating filaments. On observing this mass more carefully I 

 discovered that it was a colony of hydroids, of the suborder 

 Athecata or Gymnoblastea (PI. V. fig. 1). They are always 

 to be found on the same Mollusca, and, on all those I have 

 observed, on the same part of the shell. Their hydrorhiza 

 consists apparently of a continuous mass, and not of de- 

 tached filaments as in most other hydroids (Pi. V. fig. 

 2, c). It appears that the structure of the hydrorhiza is not 

 developed to the same degree as that of the Hydraciinia, but 

 consists simply of a mass of ccenosarc containing a consider- 



