— 134 — 



It was probably also introduced to Aarhus by a vessel; it cannot be a sur- 

 vival, as it has never been found in natural localities in the environs of 



Aarhus. 



2. Trailliella intricata Batters. This alga which was first described 

 in 1896 by Batters as found in England, has repeatedly been confounded 

 with Spermothamnion Turneri from which it, however, is easily distin- 

 guished by the presence of glandular cells and by uninucleated cells. It 

 was detected by me in some places in the Limfjord in 1901 and found 

 again in several places in the western part of that fjord in 1905 and 1906, 

 and it was gathered by others in the same water in 1908 and 1912. It is 

 thus very common and abundant in the western Limfjord. On the other 

 hand it was never observed there before 1901, though I made numerous 

 dredgings there in 1890, 1893 and 1899, and it is not represented in the 

 collections of Dr. Th. Mortensen taken from this fjord in 1895; it must 

 therefore be concluded that the species has immigrated to the Limfjord 

 about the year 1900. In the Kattegat it was first found in 1909 by Dr. 

 Henn. Petersen, namely near Hirsholm in the neighbourhood of Frede- 

 rikshavn, and it is now very common in the harbour of Frederikshavn 

 and on the reefs in the neighbourhood. The species is always sterile in 

 Danish waters. On the west coast of Sweden, Kylin has collected it in some 

 places, but it has never been observed there before 1902. It has also been 

 observed recently at Helgoland by Kuckuck. I have also observed it in 

 abundance at Arendal on the south-eastern coast of Norway in 1907 and 

 at Anuglen near Bergen on the west coast of Norway in 1916, in both places 

 sterile. The native place of the species is so far not known with certainty. 

 Apart from Northern Europe it has been found in a locality north of Sicily. 



3. Codium tomentosum (Huds.) Stackh. This species which has so far 

 not been met with on the Danish shores, was found in June and July 1919 

 at Hirsholm near Frederikshavn, growing on wood in the harbour and on 

 pebbles at the shore, and it was also found detached on the coast of Hirs- 

 holm and that of Græsholm. The specimens were well developed, up to 

 20 cm long, and provided with gametangia. This species must have been 

 introduced to Hirsholm latterly, for I have visited this islet repeatedly 

 in the years 1892 — 1905 without having met with this conspicuous alga. 

 It is curious that this alga has been introduced into the harbour of Hirs- 

 holm, which is never visited by vessels from foreign countries, while it 

 has not been met with in the harbours of Skagen and Frederikshavn, no 

 more then in those of Vesterø and Østerby on Læsø which were all ex- 

 amined in the summer of 1919. Its appearance at Hirsholm might per- 

 haps be connected with the establishment of a field of mines at Herthas 

 Flak during the war. 



4. Codium mucronatum J. Ag. In the summer of 1920 a species 

 of Codium was detected in the Limfjord where it was met with in 

 several places in Nissum Bredning, Sallingsund and Livø Bredning by 

 Dr. Henning Petersen, mag. sc. K. Spärck and cand. mag. Boye Peter- 

 sen. It was first confounded with C. tomentosum but turned out to 

 be C. mucronatum J. Ag. var. atlanticum Cotton which occurs at the 

 coasts of Ireland and Scotland. It has undoubtedly been introduced into 



