THE AERIAL ALC.Æ OF ICELAND 383 



3. Apices pointed. 



a. Yalve linear, apical area often \\'u\c f. aciila n. 1'. 



b. Sides of valve iorm regular curvcs var. lenticiilaris Østr. 



Comnion to all these varieties are the transapical fascia, the fairly 

 constant niimber of striæ (23—27 in 10/0, and the often quitc parallel 

 course of the striæ. 



Caloneis fasciata var. typica. Navicula fasciata Lagerstedt 1873, p. 34, 

 Tab. II, fig. 11. V. Heurck Syn. PI. 12, fig. 34. 



E. Icel. 78?, 85, L. 99, L. 128 - N. Icel. 140, 169, 215 — W. Icel. 

 337 — Vestmannaej'jar L. 399, L. 410. 



This form varies somewhat in size. The specimens measured from 

 various samples showcd the following dimensions: L. 20— 39,6//, br. 4,2— 

 7,7//, str. 23— 27 in 10//. The largest were found in sample 410, the 

 smallest in sample 215. Curiously enough the largest specimens showed 

 the finest striation. 



Most (5) of the samples in which it occurred were derived from 

 rocks, most frequentlj^ from piaces with trickling water. Sevcral of the 

 other samples were likewise derived from localilies with water in plenty. 

 From this we may perhaps be permitted to infer that this form does 

 not withstand desiccation very well. 



The sample containing most of the specimens was No. 410 from a 

 bird clItT. These facts would seem to show that it thrives best on a 

 mineral substratum but that nitrogenous nourishment even in plenty is 

 not harmful to it. 



— — var. fontinalis (Grun.) N. fontinalis Grun. in V. H. Syn. PI. XII, 

 fig. 33 b. 



E. Icel. L. 7, L. 128, L. 129 — N. Icel. 217. 



This variety, too, was somewhat variable in size. I have found the 

 following dimensions: L. 17— 33//, br. 4,4— 5,t //, str. 23— 27 in 10//. In 

 3 of the 4 samples it was found among mosscs. None of the localities 

 were particularly dry or could be supjiosed to provide abundnnt nitro- 

 genous nourishment. 



— — var. inconstantissima (Grun.). N. bacillnris v. inconstanlissima 

 Grun. inV.H. Syn. PI. XII, fig. 28. N. lacunarum Crun. V.II. Syn. PI. XII, 

 fig. 31. N. fontinalis Grun. ibid. PI. XII, fig. 33a (non. b!). 



S. Icel. 282. 



Xaviciila bacillaris u. inconstantissinui (hnin. as well as N. Lacunarum 

 Grun. and N. fontinalis Grun. seem to me to resemble each other greatly 

 by the regular linear form with rounded apices. The only difference 

 between them seems to me to be onc (»f size. 



In the above-mentioned sample 2S2 derived from soil by a manure 

 heap near Reykjavik in which the Diatoms were found among Prasiola 

 crisj)a, there occurred a form with the dimensions L. 29 //. br. 7,0//, str. 23 

 in 10 //. 



