BIHANG TILL K. SV. VET.-AKAD. HANDL. BAND 22. AFD. III. N:04. 13 
in transversal orbicular. Valves almost flat, with numerous 
and irregularly arranged small spines near the margin, about 
5 im 0,01 mm. Structure: fine puncta arranged in rows, ra- 
diate from the centre (where is a cluster of small, irregular 
puncta) to the periphery, 20 in 0,01 mm., and crossed by 
oblique and somewhat curved rows. Diameter of the valve 
0,025 to 0,04 mm. Endocysts are identic with Coscinodiscus 
subglobosus CL. a. GrRun. — PI. II, 14, 15, 16. 
This interesting form occurs in the same peculiar manner 
as Thalassiosira Nordenskiöldvi and may under a low power 
be easily mistaken for it, but it is distinguished by the nu- 
merous, short marginal spines, Th. Nord. having a single row 
of strong spines at a distance from the margin. 
Specimens, collected in the middle of August were fre- 
quently found containing endocysts, in all respects agreeing 
with Coscinodiscus subglobosus, so widely diffused in the polar 
basin. I have placed this species in Thalassiosira, as it re- 
sembles Th. Nordenskiöldti, but only provisionally, because 
all the forms of Coscinodiscus, Lauderia and others want a 
thorough revision, and to be arranged in a more scientific 
manner than hitherto. 
Thalassiosira Nordenskiöldii CL. This species occurs in great 
abundance in the whole polar sea, being common on the ice 
at Cape Wankarema, and forming, almost alone, the plankton 
north of Jalmal; north of Finmark, north-west of Spitsbergen, 
and there ecolouring the sea for many miles in extent. From 
there it spreds southwards, and occurs, sparingly, in the 
plankton of the west-coast of Sweden down to Kiel. A sample 
of plankton, collected the 24:th of July off Cary Islands, at 
the northern end of Baffins Bay, was very rich in this species 
and Th. gravida. From the middle of August to the begin- 
ning of October it occurred abundantly in most of the samples 
from Baffins Bay. According to ÖESTRUP it is abundant in 
the plankton of the east-coast of Greenland. 
This species is frequently found together with Coscino- 
discus excentricus which seems to comprise different forms one 
of which probably represents the endocysts of T. Norden- 
skiöldi. . 
Thalassiothrix longissima CL. a. GRUN. occurs in the Octo- 
ber-plankton of Baffins Bay. 
