KONGL. SV. VET. AKADEMIENS HANDLINGAR. BAND. 20. N:0 5. 1&1 
of Antithamnion found in the White Sea to differ in certain points from the typical «Al. 
plumula, and on this account he sets it down as a variety of this, by the name of var. 
boreale. He further elucidates Callithamnion lapponicum, which Kurrecur has first de- 
scribed, though scarcely in such a manner as to make it possible to recognize it. This 
form Gost regards as intermediate between A. plumula f. typica and f. boreale. At the 
same time, pointing out that A. plumula is closely allied to A. (Callithamnion) aimeri- 
canum, he utters the supposition that the latter alga is to be regarded only as a form 
of the former. Gopr ends his disquisition with the following words: »Es ist bekannt, 
dass A. plumula eigentlich dem Gebiete des Atlantischen Oceans und des Mittelmeeres 
angehért; im nérdlichen Ocean kommt diese Form schon viel seltener vor und zwar 
vereinzelt in sehr diinnen Biischelu von unbedeutender Grosse... Folglich erscheint sic 
fir den nérdlichen Ocean nicht als cine aborigene Stammform, sondern vielmehr als 
eine dahin eingewanderte und dabei sehr stark veranderte.» 
I quite agree with Gos in thinking A. americanum to be nearly related to A. 
plumula, especially to A. plumula var. boreale Gost. But if the former alga should not 
be regarded as a distinct species, a great many other Antithamnia described as inde- 
pendent species would on perhaps as good grounds have to subsumed as various forms 
under the same species. There are to be found transitions between A. americanum and 
A. Pylaiswi according to Farrow (New Engl. Alg. p. 123), and A. plumula var. boreale 
not seldom shows a strong tendency towards the latter species. C. corallina RKurx., 
which is connected by intermediate forms with A. plumula var. boreale, is plainly very 
closely allied to A. cruciatum, so that it might with as great reason be considered as 
a form of this species as of A. plumula or A. americanum. To this may be added 
that the distance between A. Pylaiswi, especially the form occurring on the coast of 
Norway, and A. jloccosum is not great. In specimens of A. Pylaiswi from Finmarken 
I have seen branch-systems of the last order replaced here and there in the frond by 
simple subulate branches of the shape characteristic of A. jloccosum, which makes me 
think that these two plant, considered hitherto as species, are connected by intermediate 
forms. Thus, if A. wmericanum be reduced, the reduction ought apparently to be ex- 
tended to several other species. I am of opinion that the genus Antithamnion is a young 
genus whose species are in course of development, no marked differentiation being as 
yes established and the transitional forms not having disappeared. If the common prac- 
tice with regard to such genera, Salix, Rubus a. o., is to be followed, according to 
which every form met with’ in greater quantity at different places and casy of re- 
cognition is considered as a species, both Antithamnion plumula var. boreale Gost, com- 
monly distributed in the Polar Sea, and A. plumula, A. americanum, A. Pylaiswi, A. 
floccosum and A. cruciatum ought to be regarded as distinct species. It is by these con- 
siderations that I have been led to set down the polar form as an independent species: 
A. boreale Gost. On the other side, I cannot but hold, with Gost, Callithumnion lapponicum 
Rupr. and also C. corallina Rupr. to be forms of A. boreale, as these certainly do not 
differ so much from A. boreale, as this does from A. plumula and other Antithamnia. 
A. boreale differs from <A. plumula by the different branching, by longer cells 
in the main axis and in the long branches of the frond, and by its sessile tetra- 
