Marine Plankton from the East-Greenland Sea. 323 



feci impression of the annual cycle of plankton. The following 

 samples were collected: 4 in October 1905, 2 in June, 4 in August 

 and 2 in September 1907, and one sample on July 21st 1908, when 

 the Expedition left the station. 



Table I gives the principal species and their occurrence in the 

 samples; the rarer species have been omitted (with regard to them, 

 see the systematic lists in our previous papers). 



The samples from the beginning of October 1905, which were 

 all taken in holes in the ice from water with a temperature of ca. 

 — 1-7°C.,' contain very few organisms. They are the last remnants 

 of the summer plankton, mostly dead shells of diatoms, Ceratiiim 

 arcticum and Cyttarocylis denticulata, as also a few living Chaetoceras 

 boréale, Ch. decipiens, Rbizosolenia styliformis and Peridinians, with 

 some Oithona and Nauplii. Lastly, it was interesting to find that 

 Coscinodiscus Joergensenii was in process of forming auxospores at 

 this time of year, though in very few individuals. 



The two spring samples from June 1907 were also from holes 

 in the ice (water temperature ca. — 17° C.) and contained even fewer 

 organisms. It was only in the last of the two samples that any 

 fair quantity of Melosira hyperborea was taken, its chains in process 

 of active division, as also some Oithona and Nauplii. 



The August samples (the first was taken on July 30th) contain 

 a rich diatom plankton. The principal species are Chaetoceras sociale 

 and Fragilaria oceanica, in the later also Chaetoceras diadema, Ch. 

 Wighami and Coscinodiscus subbaliens, as well as Cyttarocylis denti- 

 culata and in smaller numbers Nitzschia seriata, Thalassiosira gravida, 

 Peridinium pellucidum and P. islandicum, further Ptychocylis obtusa 

 and Tintinnns vitreus. 



The September samples show almost the same plankton, yet 

 are somewhat poorer for most species; only Peridinium pellucidum, 

 P. islandicum, Synchaeta sp., Oithona, as also Cyttarocylis denticulata 

 typica and gigantea are more frequent, and Gonyaulax triacantha is 

 added. 



Among the diatoms in September resting-spore formation is 

 found in Chaet. sociale, Ch. diadema, Thalassiosira gravida, and also 

 in Fragilaria oceanica, the resting-spores of which, however, already 

 occurred in August, though less frequently. The rare Ch. gracile had 

 resting spores in August. In Coscinodiscus subbuliens auxospores 

 were present, but in small quantity, in August and September. 



The salinity of the water was highest in June (32-3^V(io) and de- 



^ The hydrograpliical data (surface temperature and salinity) have been kindly 

 placed at our disposal by the Captain of the "Danmark", First-Lieutenant 

 H. Trolle, to whom we wish here to express our thanks. 



