10 



T. CLEVE. THE PLANKTON OF THE NORTH SEA AND THE SKAGERAK. 



B. The Skagei-ak. Samples were collected at Måseskär and Väderöboda. These 

 samples contained abundantly Ehizosolenia gracillima and Coscinodiscus concinnus; other 

 diatoms were of no importarice. Ceratiuin tripos was very common and indicates that the 

 tripos-j)lankton now was, together with a kind of southern neritic plankton, N^mct, the 

 prevailing type. Characteristic species other than these were Oithona similis, Evadne 

 Nordmani, the hitter, as usually, accompanied by Podo7i Leuckarti. The occurrence of 

 Temorella afjinis indicates a strong flow of the Baltic Current. 



July— August 1900. 



A. The Shetlands. Some samples were collected by a fishing vessel on the 2nd 

 of July at 60° 40' N. and 2° 45' W. from the depths of 200—50 m., 50—10 m. and the 

 surface. The contents of the 3 samples have been i-egistered in the following table: 



Calanus finmarchicus . . . 



Metridia Incens 



Microsetella atlantiea . . . 

 Oithona plumifera . . . . 



O. similis 



Oneoea minnta 



Pseudooalanus elongatus . . 



Salpa sp 



Cyttarocylis denticnlata . . 

 Åcanthometron catervatum . 

 Acanthonia Mulleri . . . . 

 Challengoria xipliodon . . . 



CoUozoum iuerme 



Hexalonciie hexac^autlia . . 



Ceratinm furca 



C. fusus 



Surface 



{t. 12,20 



s. 35,44) 



50-10 m. 

 (at 40 m. 



t. 11,80 



s. 35,46) 



200-50 m 



(at 200 m 



t. 9,00 



s. 35,42) 



c 



+ 



r 



+ 

 + 

 rr 

 r 

 r 



rr 

 r 

 rr 



+ 

 + 



C. longipes 



C. tripos 



Dinophysis acuta 



D. homunculus 



DiplopsaHs lenticula . . . 

 Peridluium divergens . . . 



P. ocean icum 



P. ovatuni 



Chsetoceros Lorenziamis . . 

 Coscinodiscus ocnlus iridis 

 Dactyliosolen antarcticus . 



Nitzschia lincola 



Rhizosolenia gracillima . . 



R. styliformis 



Tluilasaiotlirix longissima . 



r 



rr 



r 

 + 

 r 

 r 



200-50 m, 



(at 200 m, 



t. 9,00 



s. 35,43) 



+ 

 + 



It is apparent from this list that the plankton (styli-plankton) originated in the 

 temperate Atlantic and contained only few and rare northern forms. The occurrence of 

 Dinophysis liom.unculus and of ChaHoceros Lorenziamis at the Shetlands marks the extreme 

 northern limit for these species. 



B. The North Sea in Jvily-Angust. The North Sea was explored at the end of July 

 and the beginning of August by a number of steainers on difterent routes. The results 

 of the analysis of the numerous samples of plankton collected have been registered in 



Table III. ■ ■^: ■ ■■.!-:.- ; ■ ■'' '<-^-- •■ l^-'"-! '■ 



The determinations of the salinity prove that all kinds of water, from 35 to 24,62, 

 are represented. If the species found in the plankton be classified according to the sali- 



