832 ASTRID CLEVE, THE PLANKTON OF SOME LAKES IN SWEDEN. 



but always at only one end of eacli different individual, as in the 

 var. asterionelloides Grun. (V. H., PI. LIT, f. 9). The star-like 

 aggregate of diatoms thus formed is well adapted to be carried 

 by the waves and to keep floating in the water. From this 

 point of view, the shape is still niore perfectionated by the 

 geniculate flexion of the frustules. 



At first, one uiight feel inclined to consider this very dis- 

 tinct form a new species. 1 have not, however, found any con- 

 stant specific character that could justify such an opinion. The 

 radiate disposition of the coherent individuals is a biological 

 character occuring, as shown, also in another variety of T. fene- 

 strata, and the relative breadth of the central dilatation of the 

 valves, though used as a specific mark of distinction between 

 T. fenestrata and T. ßocculosa, ^) here at least shows to be, as 

 such, of no value (cfr. the figg. 3, 4 and 5). C. Schröter ^) 

 has referred the passively floating plankton-forms of the Oder to 

 several different, raorphological-biological types(>y Trommel-, Band-, 

 Spindel-, Scheiben-, Stern- and Sphreroid-iy^es»). T. fenestrata 

 V. geniculata does not strictly belong to any of these groups, 

 but might be regarded as a special modification of the mentioned 

 star-type (represented for instance by Asterionella formosa). It 

 also shows sorae relations with the parachute-formed Ornithocerus 

 splendidus, which has been described by F. SCHÜTT. ^) 



Tabellaria ßocculosa (RoTH.) KÜTZ., r. 



IL Spring-plankton from Virijaure. 



9. Virijaure, Staloluokta V? 1896. 



10. » Pieti-Sirkaslookta V? 1896. 



11. » Sirkasluokta-Alasluokta V? 1896. 



12. » Alasluokta (N.W. part) Vi 1896. 



^) Van Heurck, Traité des diatomées, Anvers 1899, p. 356. 



^) Ueber das Plankton der Oder, Bar. d. deutsch, bot. Gesellschaft 15, 1897, 



p. 492. 

 ^) Das Pflanzenleben der Hochsee, Kiel, Leipzig 1893, p. 35. 



