THE AERIAL ALGÆ OF ICELAND 



389 



Fig. 16. 



Navicula Brekkaensis Boye P. n. sp. 



Valva lineari, in medio inflata, apicibus rotundatis. Area 

 centrali quadrata, area apicali angiista, long. 10— 18/<, lat. 3,4— 

 3,9 /<, striis delicalissimis, mediis radiantibus, circ. 36 in 10//, 

 ceteris parallelis, densioribus. Fig. 16. 



N. Icel. 92, 169, 218, 254 - W. Icel. 336. 



It bears a close resemblance to N. conlenla, from which, J^'!",!'^"^". 

 however, it deviates in several respects. The apices are al- bovc l" n" sp 

 ways simply rounded, not capitate, the striæ, which, by the (x 1200). 

 way, are very diflicult to detect, are coarser in the inflated 

 central part than in the remainder of the valve, and radiale in this part, 

 while they are parallel in the other parts. Furthermore, N. Brekkaensis 

 has a distinct square central area. 



I have l'ound it in very diverse localities and never in any great 

 number of individuals, so it is difficult to form an idea as to what life 

 conditions are most favourable to it. 



Navicula Kotschyi Grun. Cl. Syn. I. p. 130. N. Kotschyana 

 V. Heurck Svn. PI. 10, fig. 22. Fig. nostr. 17. 



E. Icel. L. 129. 



On a rocky wall in Vestdalur near Seyc^isfjonVir I found 

 this species in great number. Originally it was found in hot 

 springs near Buda-Pest. Later on it is recorded from the 

 Bodensee and other lakes in Central Europe and from a damp 

 rocky wall (v. Schon feldt, 1913, p. 80 , and finally Hustedt 

 found it in a rock cave in Silesia in company with Pinniilaria 

 borealis and Navicula conlenla (1922, p. 98. Hence there can 

 hardly be any doubt that it thrives well as an aérial alga, 

 especially on damp rock. 



Hustedt points out i,l. c.) that in reality it has an iso- 

 lated point in the central area, like Navicula mnlica. I can 

 confirm this, having found a well-marked dot in the central 

 area which formed the termination of a faint line of small puncta. The 

 same is seen in V. Heurck's figure above referred to. The specimens 

 found by me were somewhat larger than those mentioned in Cleve's 

 diagnosis viz. up to 33// in length, 9,0 // in br., whereas the number of 

 the striæ agreed with Cleve's statements, being 18 in 10// in the 

 middle an 23 near the apices. 



Fig. 17. 

 Navicula 

 Kotscbiji 



Grun. 



(X 1200). 



Navicula mutica Kiitz. sp. collectiva. 



This species was originally established by Kiitzing, and the type is 

 regarded by V. Heurck i^Syn. PI. 10, Hg. 19) as being most probably 

 what we now call f. Goppertiana. 



The species comprises a great number of different forms all known 

 by their distinctly punctate striæ commonly 18—20 in 10//), and a 

 distinct transapical area with an isolated point on one side of the cen- 

 tral nodus. 



The Botany of Icelancl. Vol. II. 



26 



