THE FRESH-WATER CYANOPHYCEÆ OF ICELAND 315 



of developing at highly variable temperatures. Esmarch (1914 p. 273) 

 records it from earth-samples originating from clayey and marshy ground 

 at the shores of the Elb at a depth of 25 cm. 



Hveravellir is a group of hot springs situated in the middle of the 

 countr}' between Hofsjokull and Langjokull i. e. in the uninhabited region. 



Calothrix parietina Thuret. 



Bornet et Flahault, Revision I p. 366. 



E. Icel. On more or less moist rocky walls, Ekkjufell '-/t 1914, 

 Vestdalur near Sey6isfj6r5ur ^7 1914, Fljotsdalur 3% 1914. — S. Icel. 

 Geysir, temp. about 30'^ C. (Stp.i! 



Area: Eur., As., Am., Afr., Austr., Greenland. 



As far as its geographical distribution is concerned, this species 

 may be denoted as an ubiquist. Besides it is a rather pronounced aero- 

 philous alga which, however, probably requires a comparatively great 

 quantity of moisture in its substratum. It therefore thrives best in pia- 

 ces where in any case at certain seasons water trickles down over the 

 rocks or where these are dashed with spray from a waterfall or the 

 like. However, it has also been found on rocks and stones under the 

 surface of the water. 



The sample collected by Steenstru]) at Geysir contains a Calothrix 

 (attached to siliceous sinter) with threads about 10 /< in diam. and thick 

 stratifled brown sheaths that are somewhat infundibularly expanded 

 upwards. I therefore opine that it can hardly be referred to C. ther- 

 inalis as originally done by Johs. Schmidt, but that it must belong 

 to C. parietina. However, it cannot be identical with the following va- 

 riety as this is said to be characterised by its colourless sheaths. 



Calothrix parietina Thur. var. thermaiis G. S. West. 

 West 1902 p. 243, tab. 439, ligs. 17-20. 

 Hveravellir, temp. 24^ C. On rocks and stones. 



Calothrix thermaiis (Schwabe) Hansg. 

 Bornet et Flahault, Revision I p. 368. 

 Mastichonenia thermale Kutz. Tab. phyc. II, lab. 46, lig. I. 



W. Icel. Sturlureykir, on siliceous sinter at little Hver (temp. 76°); 

 the algæ were not overtloved by the water. ^/s 1914. 

 Area: Eur., Afr., N. Am., S. x\m. 



The mentioned sample consists in the main of a Calothrix which 

 I refer to C. thermaiis in spite of the threads being often somewhat 

 thicker ^up to 13.2 u) than they usually are in this species. 



Has hitherto only been found in hot springs. 



II. Dichothrix Zanardini. 



Dichothrix Orsiniana (Kutz.) feorn. et Flah. 



Bornet et Flahault, Revision I p. 376. Lemmermann 1910 p. 247. 

 Rabenhorst Algen nr. 1177. 



21* 



