18 P. T. CLEVE, THE PLANKTON OF THE NORTH SEA ANt) THE SKAGERAK. 



It is of interest to note how different the two first saraples are, although they had 

 been collected at a distance of about one degree. The first sainple consists of didywus- 

 plaiikton, or of forms from the southern North Sea, and the second of ^rzpo.s-plankton or 

 from the northern North Sea. ViOih. are comparatively richer than the following three, 

 which eome from a raixture of water from the southern and northern North Sea. 



Seasonal distribution of the Plankton-organisms. ' 



Appeiidiculaiia. 



Fritillaria boroalis Lohm. — • March: M. rr. April: Sk. r; W. of the Danish Penin- 

 sula to Sk. and V. r. M. r. November: Sk. rr. 



Oikopleura dioica Fol. — Ajjril: between Dogger Bank and Sk. r. May: N. E. of 

 Scotland -f-. June: M. r. Jidy, August: Scotland to Sk. v; S. of Dogger Bank; W. of 

 Jutland. M. c. V. r. September: M. +, V. r. October: M. and V. +. November: M. r, 

 V +. Vinga (30 m.), W. of Jutland, Sk. r. December: V. rr. 



Pteropoda. 



Cleodora pyraniidata Lin. — June: Shetlands ce. 



Spirialis retroversa Fi.em. — November: W. om Limfjord, r. Vinga (30 ra.) r. 



Amphipoda. 



Aniathilla aug-ulosa Rathke. — November: V. cc. 



Caprella septentrionalis Kröyer. — Marek: V. r. 



Parathemisto oblivia Kröyer. Fehruary and March r. 



Proto pedata Leach. — Fehruary: Mouth of Scheldt rr. July — Aui/ust: W. of Lira- 

 tjord r. December: V. -|-. ■.u, , : .■ ' . , , ' ■ 



Cladocera. 



Evadno Nordmani Lovén. — April: W. of Jutland r. May: M. cc, V. r. Jime: 

 Shetlands -|-' ^^- '-'cc^ V- ccc. Jtdy — August: Orkneys and Firth of Tay to southern 

 Norwuy; M. r, V. c. September: M. c, V. -)-. October: M. r. Novemher: M. and V. r. 



''- I use tlio :i))l)r('via1ioii M. l'nr Måseskär, V. tor Vädt^röboda and Sk. for Skagoii. 



