12 P. T. CLEVE, DIATOMS FROM BAFFINS BAY AND DAVIS STRATT. 
Nitzsehia frigida GRUN. is a true plankton diatom, which 
occurs in irregular, branched chains as Thalassiothrix Frauen- 
feldit. It was found sparingly from May to the middle of 
August and is characteristic for the polar seas. 
Nitzschia lxvissima GRUN. was found in isolated specimens 
in most of the samples. Characteristie polar-diatom. 
Nitzschia polaris GRUN. was found in some few samples. 
Doubtful as a plankton-diatom. 
Nitzsehia seriata CL. (Vega P1. XXKXVIII f. 75) is a cha- 
racteristic plankton-diatom, occurring in rows of coherent fru- 
stules. It was found abundantly in May, scarcer later on in 
the year. It was also found in Davis Strait in October, but 
rarely. It is not mentioned by ÖESTRUP as occurring on the 
east-coast of Greenland, but occurs on the west-coast of Swe- 
den in the month of February. 
Pleurosigma Stuxbergii CL. and its variety rhomboides OL. 
occur sparingly in most samples; are no doubt characteristic 
of the plankton of the polar seas. . 
Podosira glacialis (RUN. (Pod. horm. var. glac. GRUN. in 
Franz Josefs Land. Diat. PI. IV f. 32). In the plankton of 
May a form occurs abundantly, which in size and strueture 
seems to me to agree with the fig. of above in GRUNOW'S 
work, but as the valves are almost plane I cannot consider 
it a variety of P. hormoides, but rather of P. HFebigeri 
Grus. There occurs constantly near the margin a small 
pseudonodule, not to be seen on GRUNOW's figure. It is no 
doubt nearly related, perhaps a large form only, of Thalas- 
siosira gravida named bellow. — Pl. IT, 17—20. 
Rhizosolenia hebetata Barn. This species, which I have 
seen abundantly only in the plankton of Behring Sea, occurs 
very rarely in a sample collected at the end of September. 
Some few specimens were also found in the October-plankton 
from Davis Strait. 
Rhizosolenia setigera BTW. occurs sparingly in most samples. 
Rhizosolenia styliformis Brw. This species, so abundant in 
the northern and middle Atlantic, was met with, in a few 
specimens only, in many of the samples. It is evidently no 
polar form and has been found as weil in the Mediterranean 
as in the Indian Ocean. 
Thalassiosira gravida CL. N. Sp. Cellules coherent by a 
central mucous thread, in sagittal view with quadrate outline, 
