THE AHHIAL ALGÆ OF ICELAND 



401 



Pinnularia appendiculata Ag. var. irrorata Grim. Van Heurck Syn. 

 PI. VI. iiy. 31. 



E. Icel. 8. L. 41, L. 61, 78, 124? 

 L. 254, L. 256 — N. W. Icel. L. 269 



\. Icel. 135. 169, 217, 218, L. 253, 

 W. Icel. 307, L. 321, 336. 



On measuring Van Heurck's figiire (1. c.) I found the following 



dimensions: L. 18,9//, br. 3,4 //, str. 25 in 10//. Tliis shows a fairh' close 



agreenient with a nuniber of speciniens which I loiind in the Icelandic 



samples. One of these is shown in fig. 22. Its dimensions 



were: L. 15,5//, br. 3,9//, str. 23 in 10//. The valve was in 



the main linear, with a thickening in the middle and at the 



ends. The median striæ were somewhat more strongiy marked 



than the rest. The striæ radiated in the middle, converging 



slightly at the apices. Apical area narrow, only slighlly ex- 



panded around the central nodiile. The only particular in Fig. '22. 



which I find some deviation from Van Heurck "s ligure is Pinnularia 



that the median striæ are somewhat more shortened in that "PP^'^dici- 



figure than in the specimens observed by me. Cleve in- " ." n-^^'"* 



. , ■ • . , • T^- , • ... irrorala 



cludes the present vanety withm Pinnularia appendiciilala. It Grun. 



seems to me that he goes too far. In the material I have (X 1200). 



examined I have not found anj^ intermediate forms. In sample 



169, however. I found a form approaching P. Ociiliis Østr. by its strongiy 



capitate ajiices, but ditTering from that form by its smaller size and 



liner striation (L. 15//, br. 4//, str. abt. 24). In other samples I found 



shorter specimens whose apices were very indistinctly capitate. 



I found the present form in rather diverse locatities, both among 



mosses and algæ on purely mineral ground. in piaces near houses 



abounding in manure, and near hot springs. 



Pinnularia boreaiis Ehrb. Cl. Syn. II, p. 80. V. H. Syn. PI. VI, fig. 3, 4. 

 A. Schm. Atl. PI. 45, fig. 15—21. 



E. Icel. 4, 7, 8,14,15, 28, L. 40, L. 41, L. 61, L. 68, L. 69, 70, L. 77, 

 78, L. 85, L. 92, 112, L. 113, 114, L. 121, L. 123, L. 125. L. 128, 129, 131 - 

 N. Icel. 135, 137, 138, 140, L. 160, 161, L. 162. 169, 173. L. 182, 184, 

 L. 185, L. 196, L. 217, L. 218, L. 219, L. 241, 242, 252, L. 254 - N. W. Icel. 

 L. 268, 269 — W. Icel. 298, 307, L. 309, L. 321, L. 327, 336, 338 — S. Icel. 

 282, L. 295, L. 352, L. 353, L. 372, 373, 381, 387. 



P. boreaiis is a highly variable though generally easily recognisable 

 species. Cleve mentions (1. c.) that it shows a transition to P. lala, and 

 conversely I should think that transitional forms to P. Balfoiiriana might 

 be found. In the course of time a numbcr of diflerent forms, oflen 

 termed varieties, have been described and figured. Ehrenberg already 

 mentions some (see de Toni Syll. Alg. Vol. II, Sect. I, p. 20). Some have 

 been mentioned later and described by more recent authors, olhers have 

 not been mentioned. Subsequently a number of forms were ligured in 

 A. Schm. Atl. (1 c.) without any special designation. Moreover a couple 

 of forms have been described by Pantoczek and Grcguss (Greguss 

 1913, p. 214, Taf. VII, fig. 68, and Taf VI, fig. 39 and by Carlson (1913, 

 ]). 21, Taf III, fig. 15) I shall not make more detailed mention of all 



