623 



disposal. I came to the conclusion Ihal Huitfelt-Kaas is right; the 

 alga in question is a distinct species, which dillers considerably 

 from P. cinctum in the distribution of ils piates, and is, moreover, 

 somewhat different (Vom it in ils whole shape, and the structure 

 ol* the piales. I have given a diagrammatic figure as a supplement 

 lo Huitfelt-Kaas's figure showing the distribution of the piales on 

 the dislal limb (Ihe apical hall); by comparing this figure wilh 

 A. I. Seh illing's 1 diagrammatic lignres of ihe Peridinium-species, 

 il will be seen thai the present species occupies rather an isolated 

 position, the arrangement ol" the apical piates differing considerably 

 from thai of the olhers, il resemhles P. cinctum in one particular 

 only, that holli of them are destitute of apical pore, which is pre- 

 sent in all the other species. 



Moreover, on looking through the different works, \ve (ind thai 

 a great many of the writers entertain very conflicting views rc- 

 garding the definition of the Iwo common species P. tabulatum and 

 P. cinctum, and many statements of the occurrence of P. tabulatum 

 as a plankton-organism must unquestionably be due to its having 

 been confounded with P. cinctum, which appears to be by far the 

 most commonly occurring limnetic species, while P. tabulatum be- 

 longs more particularly to small collections of water (slonghs, 

 puddles, etc.) 2 . 



From a plant-geographical point of view it is extremely inter- 

 esling that P. Willei occurs in the Færoes, and it is of no less in- 

 lerest that I have also found it in Iceland, having observed it in a 

 plankton-sample which Mr. Jonsson gave me to investigate. Its oc- 

 currence mav now be expected also in the Scottish lakes, and, in laet. 

 its distribution mav be greater than is known. K. M. Le vander 3 

 has recently recorded it from the lakes of the Murmanian coast (Pen- 

 insula of Kola) and from those of southern Finland, and O. Borges 

 (1. c. p. 23) records of P. cinctum from the lakes of northern Sweden 

 douhtless refers to this species. It will only be justifiable to express 

 an opinion as to its plant-geographical importance, when the investiga- 

 tions bearing on ils distribution are carried out more extensively. 



1 Schilling. AI.: Die Siisswasser-Peridineen. — Flora o. allgem. botan. Zei- 

 tung, 1891, Heft 3. 



2 e. g. , the figures by G. Klebs (Organisation einiger Flagellaten -Gruppen, 

 Unters. a. d. Botan. Institut zu Tubingen, I, 2, 188.'}. PI. 2, figs. 22— 24, 28) are 

 named /'. tabulatum, but belong without doubt to P. cinctum. 



;! Levander, K. M.: Beitråge zur Fauna und Algen flora der sussen Gewasser 

 and der Murmankuste, p. l(i. — Acta pro Fauna & Flora Fennica, XX. 8. 1901. 



