KONGL. SV. VKT. AKADKMIENS HANDLINGAK. BAND 32. N;0 7. 11 



II. Plankton of tlie Skagerak in 1897. 



During the year 1897 samples wcre gathered two to four times iu each raonth at 

 Måseskär, in June, July and August on inany different spöts along the Swedisli coast, 

 in September on the route Vinga to Oxö in Norway, in October and November on 

 several points in the Skagerak, and finally in December at some points in the Skagerak 

 and in Gullmarfjord. 



The animals in these collections, made from January to September, have been 

 examined by Dr. C. Aurivillius, who has already published the results. ^ The samples 

 gathered from September to the end of the year have been examined by me, also as 

 regards the animals. An extensive amount of observations have thus been accumulated 

 during the year 1897 and will be discussed in the following pages. 



Ith Period. Jan. 4*^ — Febr. 8*^. The collections from Måseskär prove that during 

 this period the ruling plankton belonged to the tricho- and ^r/^^os-types. Animals ai-e 

 scarce. Among them we note the northern or arctic Fritillaria borealis, Tintinnus den- 

 ticulaiits, Tintinnopsis ventricosa and the euryhaline Acartia longir envis, Centropiujes hamatus 

 and Temora longicornis. Some few specimens of the southern neritic plankton, as Cory- 

 cceus anglicus, Oithona siviilis, Paracalanus parvus and Sagitta bqnmctata, Avhich are 

 lingering remnats from the summer, disappear during March and April. 



Of dinoflagellates Ceratium trrpos and its associates in the tripos-plankton are not 

 rare. The northern Cerat. trijj. var. lomiipes is not rare. 



Almost all diatoms are northern or arctic forms, as: 



Biddulphia aurita r. Coscinodiscus oculus irdis + . 



Chaitocerof; borealis var. Brightwellii + . C. polychordus r. 



C. debilis + . '-=-;^^:^ Skeletonema costaiuin + . 



C. scolopendra r. Thalassiothrix Frauenfeldii c. 



C. siinilis r. T. longissima c. 



Among southern species we note some scai-ce specimens of Guinardia Jiaccida. 



lind Period. February 23'^ to April 1*. This period is characterized by an in- 

 crease of arctic forms and by the decrease of the tricho- and tripos-types. In the be- 

 ginning of the March the chgeto-plankton sets in. 



Among the arctic and northern species Ave note as most characteristic the following: 



Dinobryum pellucidum. Chcetoceros teres. 



Cha^toceros borealis var. Brigtkwellii. Coscinodiscus oculus iridis. 



C. debilis. Nitzschia seriata. 



C. diadema. Rhizosolenia obtusa. 



C. hiemalis. R. semispina. 



C. socialis. Thalassiothrix Nordenskiöldii. 



1 »Dic Plauktoufaima des Skageraks>., K. Sv. Vet. Akad. Haudl. Band 30. N:o 3. 1898. 



