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form, the typical, Atlantic C. tetragonum (With). This apparently rather variable 
species may very likely comprise a number of elementary species, but as it is im- 
possible for me to distinguish them, it is preferable to distinguish varieties or forms 
within the larger species. 
The typical C. fetragonum has not been found at the shores of Denmark. But 
plants that must be regarded as forms of this species have been met with in two 
distinct groups of localities, the one in the neighbourhood of Frederikshavn and 
Hirsholmene in the Northern Kattegat, the other at the North coast of Sealand 
Fig. 232. 
Callithamnion tetragonum var. divaricata. From Hirsholmene. A, part of stem with branches. B, branch. C, branch 
with procarp; the two auxiliary mother-cells are visible. A 50:1. B 47:1. C 260:1. 
from Gilleleje to a place a little north of Helsingor. As the specimens from these 
two groups of localities are different from each other, they may be mentioned par- 
ticularly. 
The species is easily distinguished from the other Danish species by its pointed 
pinnule which never terminate in a hair and by the cells being multinucleated to 
the top or with the exception of a few of the uppermost cells. 
Var. divaricata. 
The species has been found several times in the neighbourhood of Frederiks- 
havn and at Hirsholmene but only in a few and small specimens, 1,5—2,5 cm high. 
They pretty much agree with var. brachiata in the structure of the pinnulæ, but 
41* 
