M. C. Mereschkowsky on the Hydroida. 331 
Localities.—1. Island of Solowetzky, on a Balanus (depth 
unknown) ; 2. Not far from the Orlow promontory, 67° 17’ N. 
lat. and 41° 35’ KE. long., at a depth of 35 fathoms ona 
gravelly bottom, attached to Flustra (June 28) ; 3. Glacial 
sea, Mourmansky bereg, Gaurilowo, Stanowischtjé (from M. 
Danilewsky, in the collection of the Museum of the Academy 
of Sciences of St. Petersburg). 
This species has long been known; but M. Sars and Mr. 
Hincks have regarded it as simply a polar variety of Sertularella 
polyzonias. Nevertheless, even by its appearance to the 
naked eye, by the habit, it is always very easy to distinguish 
this species from every other species of the genus Sertularella; 
and this distinction is produced principally by the enormous 
hydrothece, which are often twice the length of those of S. 
polyzonias. And besides all this, it must be taken into con- 
sideration that, among all the Hydroids of my collection, I do 
not find a single one that presents a form intermediate be- 
tween S. polyzonias and S. gigantea, which I possess from 
three different localities. Hence this character is very con- 
stant, and is characteristic of the northern seas. Neither Mr. 
Hincks, nor M. Sars, nor MM. Smith and Hagen say a 
single word as to intermediate forms;.so that I am led to 
regard the var. gigantea of S. polyzonias as a distinct species, 
as constant as any other, and having characters sufficiently 
salient to enable it to be recognized with facility. Besides its 
size, this species is further characterized by the form of the 
hydrothece, which are much elongated and often have three 
or four ribs, by the margin, which is always adorned with 
several (sometimes eight or even ten) ledges, giving it a 
very peculiar aspect, and, lastly, by the mode of ramification. 
All this will be better understood from figs. 6 and 7 of 
Plate XIV., especially if these drawings be compared with 
that of S. polyzonias given by Hincks*. 
Usual length of the colony 3-4 centims. Length of the 
hydrotheca 1:3 millim., its breadth 0°52; space between two 
successive hydrothece along the stem 0°63. 
Sertularia albimaris, nov. sp. (Pl. XIV. figs. 3-5.) 
Hydrorhiza composed of a continuous layer, produced by 
the confluence of an ordinary ramified hydrorhiza in a single 
plane; so that the thickness of the layer does not exceed the 
diameter of the tubes of the hydrorhiza. The surface of this 
* Hincks, Hist. of Brit. Hydr. pl. xlvi. fig. 1. Ihave Sertularella 
polyzonias from the Black Sea; so that I have been well able to compare 
the two species; and it is strange that Mr. Hincks did not find it possible 
to separate these two very different forms. joe 
