THE AERIAL ALGÆ Ol' ICELAND 



393 



Fig. 18 



Navicula 



mutica Ki'itz. 



This form may be describcd as follows: Valves lanceolale, with 

 obtuse apices, somewhat gibbous in thc iniddlc. L. 37/(, br. ll/<, str. 

 18 in 10 /^ puncta 14 in 10 /r Raphe somewhat shortened at apices; 

 apical area narrow, at each of the apices expanded to a 

 round area, in the middle to a square transnjjical area with 

 an isolated point on one side. In the girdle view the cell 

 is seen to have convex faces. It is probably the same form 

 as is described by Pi ay fa ir (I. c), even thoiigli there arc 

 certain deviations. Thiis one figure sliows a spccimen desti- 

 tute of transapical area, wliile the raphe is shown reaching 

 to the verjf apices of the valvc. However, the description and 

 figures are altogether somevv-hat incomplete, amongst other 

 things information as to the striation of the valves is entirely 

 lacliing. 



A form verj' miich resembling the one here described is 

 mentioned and figured by Zimmermann (1919, p. 99, PI. III, 

 fig. 4. Navicula mutica v. rhombica). It diflers from this spe- 

 cies, however, by its undulate side walls and finer striation, 

 as also by being smaller. Bristol (1920 p. 69, fig. 9,1) ^^^^ '"frhomboi- 

 likewise a figure of a form of Navicula mutica bearing great dea Playfair. 

 resemblance to the present form. Finally Hu stedt mentions (X 1200). 

 a similar form (1921, p. 153, Taf. I, figs. 13-15), opining 

 that it is identical with N. Lagerheimii Cl. (1894, p. 101, PI. VII, fig.ll). 

 I doubt the correctness of this Identification, however, and I have tried 

 to procure original material from the Riksmuseum at Stockholm where 

 Cleve's collections are preserved. This was not possible, however, since 

 the collection has not yet been arranged. One of Hustedt's figures 

 corresponds closely to N. mutica var. rhomlnca Zimmerm. in appearance, 

 the other two agree with the form here described which I must provi- 

 sionally regard as a separate formå that cannot be identified with 

 N. Lagerheimii until Cleve's original preparations or material of this species 

 have been examined. The same form will be found in Van Heurck's 

 Types No. 114 together with a typical N. mutica var. Guppertiana corre- 

 sponding to Van Heurck Syn. Tab. 10, fig. 18b. 



That the form mentioned here, like the other forms of Navicula 

 mutica, is of pronounced aerial occurrence is beyond doubt, and since 

 it occurs in company with f. Cohnii in all 3 samples, it probably requires 

 the same life condilions as the latter in order to thrive well. 



f. Wulffii Boye P. Boye Petersen 1924 II, p. 312, fig. 2. 



N. Icel. L. 182, 241. 



This form is characterised by its perfeclly symmetricai valves which 

 are oblong, slighlly rostrate, with broadly rounded apices. L. 17—27,«, 

 br. 6— 8^<, str. in the middle 14—18 in 10//, closer towards the apices, 

 abt. 24 in 10//. 



Area: Only known from Greenland. 



Navicula nitrophila Boye P. n. sp. 



Valva ovalis vel lanceolata vel curte linear!, apicibus rotundatis vel 



