M. C. Mereschkowsky on the Hydroida. 337 
Polyserias Hincksti, nov. sp. (Pl. XV. figs. 1-4.) 
mere glacialis, Mereschk. Ann, & Mag. Nat. Hist. vol. xx. (1877) 
p. 226, 
Colony rather rigid, plumiform, attaining a length of 20 
centims. and a breadth of 10 centims. The principal stem is 
angularly bent, and only bears two kinds of hydrothece. 
From each angle issues a branch, which at first forms with 
the main stem an angle of about 45°; but afterwards this 
angle enlarges more and more until the position of the branch 
becomes vertical to the main stem. ‘The branches are long, 
cylindrical, attain a length of 6°5 centims., and become shorter 
im proportion as they approach the apex of the colony. They 
are attached by means of a short and slender peduncle ; their 
arrangementis alternate and in the same plane (Pl. XV. fig. 1). 
The hydrothecee upon the branches are always arranged in six 
rows, as in the preceding species, and in the same alternate 
manner; but here each pair of rows (fig. 2) forms a distinct 
system, separated by a small interval not occupied by hydro- 
thece. The roundness of the branches is more distinct in this 
species, as also the rows of hydrothece. The thickness of 
the branches is very considerable, and still greater in the 
youngest. The hydrothece are oval, a little wider below, 
with a more or less regular oval aperture ; they are immersed 
in the stem for their whole extent, and their neck does not 
project outwards. In the lower part of the hydrothece 
there is a small tube, which constitutes the communication 
between the hydrotheca and the central canal which traverses 
the whole length of the branch. Colour of the branches pale 
yellow, that of the main stem dark brown; the points of the 
branches are not of darker colour as is usual in P. mirabilis. 
Gonophores in the young state (fig. 4) in the form of a re- 
versed cone, just as in P. mirabilis, but generally smaller. 
In the adult state (fig. 3) they retain their conical form, but 
the cone becomes larger and more elongated; below, it is 
attached by a short peduncle; above, it is truncate with the 
margins much rounded, and furnished with a tube of very 
inconsiderable length, which is scarcely observable, and much 
narrower than in the preceding species. The gonothece of 
this species are never present in such abundance as in P. 
mirabilis. 
This species, the largest that I am acquainted with in the 
White Sea, is distinguished from the preceding by the greater 
breadth of the colony, due to the extreme length of the lateral 
branches, by the much lighter colour, and especially by the 
stout, cylindrical form of the branches, the surface of which is 
