Radtolaria of the Arctic Expedition, 1875-76. 437 
53. Polystomella arctica, Parker & Jones. 
(Pl. XXI. fig. 13, a-d.) 
An essentially boreal species, its distribution probably not 
extending further south than Shetland. It is a large, coarse, 
thick-shelled modification of the type, most nearly related to 
P. striatopunctata. There are, however, certain structural 
peculiarities observable in mature specimens, the most impor- 
tant of which is the duplication of the sutural apertures. In- 
stead of the single line of orifices immediately over each 
septum, there are frequently two parallel rows, which, if 
the sutures are marked externally by raised bands of ex- 
ogenous deposit, appear one on each side of the limbation. 
From the exterior it appears as though the two rows of 
pores opened respectively into the two adjacent chambers ; 
but with a little care sections may be made (fig. 13, d) 
showing clearly that this is not the case, but that the 
double tubulation is the result of the lengthening and bi- 
furcation of what was originally a simple orifice. The 
horizontal section of the entire shell (fig. 13, c) shows its 
general structure. The laminated thickening appears to 
be confined to the last convolution, and to be caused by 
the chamber-wall of some of the segments being extended 
over that of the previously formed chainbers, as in the 
Nummulite. The investment of the later chambers is there- 
fore thinner than that of those preceding them, the last formed 
being the thinnest. 
The typical Polystomella crispa, so common in the shallow 
water of temperate latitudes, does not appear at all in the 
material from these polar localities. It seems to be replaced 
by P. arctica, with P. striatopunctata in still larger numbers ; 
and these pass by insensible gradations into the various forms 
of Nonionina. 
RADIOLARIA. 
Here and there in the finer portions of some of the sound- 
ings the siliceous tests of Radiolaria were observed ; but at one 
station only, and that the most northerly of all, were they 
met with in any abundance. In most cases there was no great 
difficulty in assigning the various forms which were obtained to 
their generic types; but it was found impossible to determine 
the species satisfactorily from published authorities. Under 
these circumstances, the natural course to pursue was to 
forward the mountings to Prof. Haeckel, of Jena, for his 
opinion on the more doubtful specimens. The learned Pro- 
