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of the cells is usually about four-sided and their longest diameter, parallel 

 with the longitudinal axis of the plant, is about 1 4 fx long. The thickness 

 of the frond in transverse section is about 17//. The branches of the 

 last order are sometimes consisting of only one cell-row, but usually they 

 are for the most part composed of two cell-rows and only towards the 

 apex of one. These specimens, gathered in August, are repeatedly branched 

 and have no proliferations. They occurred in the lower litoral region 

 where they formed widely extended, prostrate strata on a muddy sand- 

 bottom, sometimes in company with Dictyosiphon foeniculaceus. 



The specimens gathered by Strömfeit at Eyrarbakki in S. Iceland and 

 determined by him as Enteromorpha compressa f. racemosa, are somewhat 

 lower than my specimens, the branches somewhat broader and the frond 

 thicker (up to 30 fx). The cells are arranged in rows and their shape 

 somewhat resembles" that of my specimens. Strömfelt's plants seem to 

 agree better with the var. Agardhiana Le Jol. (1. c.) than the var. 

 Rothiana, which, I think, is to be regarded as the typical E. clathrata. 

 Some of Strömfelts specimens had abundantly occurring trabecular , as 

 described above in E. intestinalis f. genuina and f. proliféra. 



At Olafsvfk and Vestmannaeyjar I met with a form , which I have 

 with some doubt, referred to this species. This form differs from var. 

 Rothiana by a broader and thicker (up to 40 fx thick) frond, by less 

 regularly shaped cells and by the occurrence of proliferations. It is, I 

 think, closest connected to var. Agardhiana, from which it essentially 

 differs by the abundantly occurring proliferations. In many respects it highly 

 reminds of E. intestinalis f. proliféra, but differs from it by more abundant 

 occurrence of genuine branches. Some of my specimens have cells, seen 

 from the surface, resembling those of E. clathrata and in transverse section 

 resembling E. intestinalis f. proliféra. The proliferations occur more abund- 

 antly in the lower part of the frond and the cells are of more irregular 

 shape below,, having sometimes the longest diameter, parallel with the 

 longitudinal axis of the frond, amounting to 25 fx. In the upper part of 

 the frond the cells often are arranged in more or less distinct rows, but 

 in the lower part they are usually without any order. The shape of the 

 cells is often nearly regularly four-sided in the younger branches. Some 

 specimens, which I have referred to E. intestinalis f. proliféra, and espe- 

 cially those collected by L. K. Rosenvinge at Reykjavik, resemble in many 

 respects this form. It occurs in the middle part of the litoral region 

 and is often growing gregariously in lower places in the Fucus zone. 



E. I c el. Djüpivogur. 

 NW. I c el. Rroddanes. 

 SW. I c el. Olafsvfk. 



S. Icel. Eyrarbakki (Strömfeit); Vestmannaeyjar. 



Botanisk Tidsskrift. 25. Bind. 23 



