Marine Diatoms 25F 
Nitzschia polaris Grun. 
Grun. Diat. F. Jos. Land, Pl. 1, figs. 62-63. 
1 ie in a dredging from Station 29g and a plankton haul from same 
ocality. 
Nitzschia seriata Cl. 
Gran Nord. Plankt., p. 130, fig. 174. 
Rather infrequent in two plankton hauls, Stations 12b-c and 422. 
Nitzschia Sigma (Kiitz.) W. Sm. 
Van Heurck Syn., Pl. 66, figs. 1-9. 
The type form occurs but is uncommon; many varieties were found, as.var. 
Habirshawii (fig. 4 above) and var. Sigmatella (fig. 6 above). Found at Stations 
20b-c, 41, 43b, 43c. 
Nitzschia socialis Greg. var. Kariana Grun. 
Cl. and Grun. Arct. Diat., Pl. 6, fig. 108. 
Found at Station 23. 
Nitzschia Weissflosii Grun. 
Perag. Diat. France, Pl. 76, figs. 3-4. 
Only one specimen found, Station 41. 
Plagiogramma Grev. 
Plagiogramma Gregorianum Grev. 
Perag. Diat. France, Pl. 82, fig. 7; Micro. Journ., 1859, Pl. 10, figs. 1-2. 
Some authors change this to P. staurophrum (Greg) .Heib., perhaps correctly; 
see Greg. Diat. Clyde, p. 497, Pl. 10, fig. 37 and De T. Syl. Alg., p. 718. 
Found at Stations 20b-c and 27s, scarce. 
Pleurosigma W. Sm. 
Pleurosigma angulatum W. Sm. 
W. Sm. Brit. Diat., Pl. 21, fig. 205; Perag. Pleuro., Pl. 5, figs. 3-5. 
This common species is here uncommon; only a rare specimen in one 
dredging, Station 29g. 
Pleurosigma balticum (Ehr.) W. Sm. 
W. Sm. Brit. Diat., Pl. 22, fig. 207; Perag. Pleuro., Pl. 7, fig. 20. 
Rather abundant, especially at Stations 20b-c, 23 and 27s, large and typical 
specimens. 
Pleurosigma Fasciola (Ehr.) W. Sm. var. sulcata Grun. 
Cl. and Grun. Arct. Diat., Pl. 4, fig. 75. 
This seems to be a strictly polar variation of the type. Found at Station 
23. 
Pleurosigma formosum W. Sm. 
W. Sm. Brit. Diat., Pl. 20, fig. 195; Perag. Pleuro., Pl. 1, figs. 1, 6. 
All the specimens below normal size; only in one dredging, Station 20b-c. 
Pleurosigma glaciale Cl. 
Cl. Vega Diat., Pl. 35, fig. 18, see p. 476. ; 
Found in plankton haul at Station 29g. Length of my specimen 0-13 mm. 
Pleurosigma Grundlerii Grun. 
Perag. Pleuro., Pl. 6, fig. 1. 
It is rather close to P. rigidum W. Sm. See other figures on same plate. 
Found only at Station 23. 
