BIHANG TILL K. SV. VET.-AKAD. HANDL. BAND 22. AFD. III. N:04. 11 
Fragilaria cylindrus GRUS. This species, found on the ice 
of Cape Wankarema, Franz Josefs Land and the east-coast 
of Greenland, was very abundant in the May-plankton, but 
became scarce later on in the year. It is a species no doubt 
very characteristic of the polar sea-plankton. It occurs in 
bands as the other species, which do not differ in appea- 
rance. It is only on boiled specimens that one can distin- 
guish the different pelagic species of Fragilaria. 
Fragilaria oceanica CL. This species appeared in large 
masses in May, became later more scarce, but reappeared in 
Davis Strait in October. Fragilaria oceanica is a species 
characterizing the plankton of the polar sea and the northern 
Atlantic. It is difficult to define its exact distribution as it 
may be easily mistaken for other species, if not boiled with 
acids. 
Lauderia confervacea CL. N. Sp. dCellules coherent in long 
and very thin threads, diameter 0,01 mm. Length of the 
frustule 0,015 to 0,03 mm. HSpines at the periphery of the 
valve about 10 in 0,01 mm., very short. Divisions of the 
zone are seen only with difficulty. — P1. IT, 21. 
This very delicate form, which occurs sparingly in some 
samples from Baffins Bay, is entirely destroyed on boiling with 
acids and greatly altered by ignition. 
Melosira (nummularia var.) hyperborea GRUN. occurs sparingly 
in May, June and August. It is a characteristic form of the 
polar sea. 
Navicula septentrionalis OEstrRUP (Meddelelser om Grönland 
RÖVEN S95 pp 430rP1A VELISf NOT) ANS species! ist a very 
characteristic plankton-form, and occurs in long bands of firmly 
united frustules, which are so thin that they are destroyed 
on boiling with acids. I have not succeeded in resolving the 
structure. It occurs not rarely in May, but is very scarce 
in August. 
Another Navicula occurred together with this species in 
a similar manner. Dimensions: sag. ax. 0,015; tramsv. ax. 
0,004; long. ax. 0,005 mm. I was not able to resolve the 
structure of this species. On ignited specimens some very 
fine hairs were seen issuing from the central nodule. I call 
it provisionally N. pelagica. — P1. I, 9. 
Nitzschia Closterium W. Sm. occurs sparingly in most samp- 
les. Probably a cosmopolitan species. 
