lagoon of Ghristianssted is a long narrow bay which to the East 

 of the town extends itself in an easterly direction into the land, sur- 

 rounded by low hills. It is a typical lagoon with mangrove vegeta- 

 tion; the bottom consists of clay mixed with sand, the water is not 

 clear and rather shallow, and it is connected with the sea by a 

 little shallow passage only. In the large bay behind Longreef west 

 of the town, the water is on the contrary clear and crystalline, as 

 both towards the West by a smaller passage and towards the East 

 by a larger one there is a connection with the sea; the latter also 

 at high water washes over the reef. The bottom here is dazzlingly 

 white coralsand and the depth seldom more than two or three 

 fathoms, so that everything growing at the bottom may be 

 easily seen. 



Here on this loose sandbottom a rich Alga vegetation is 

 growing, not rich in species, it is true, but on the other hand 

 rich in individuals. We here find a. group of Algae which are 

 adapted to establishing themselves and growing on the loose bottom 

 (psammophile and pelophile Algae) to which we have no counter- 

 part in the northern seas. To be sure, the localities where these 

 Algae grow are rather protected against the open sea by the coral- 

 reefs or by being situated in the bays, and we therefore can not 

 compare them with the sandy, sterile west coast of Jutland f. i. 

 where the sandy bottom during gales is in a motion so lively, 

 that even in a tropical climate we could not expect to find any 

 vegetation at all ; but even in more protected localities with sandy 

 or muddy bottom in the North, fixed Algae as is well known, are 

 entirely wanting, they occur at once however, where a stone or 

 some other firm object is found , to which they can attach them- 

 selves. This Alga vegetation established and growing in the loose 

 bottom is peculiar for the warmer seas. 



This Alga vegetation may be divided in two groups; the vegeta- 

 tion of the creeping Algae which is represented by the genus 

 Caulerpa and that of the Algae fixed to the same spot with the 

 genera Penicillus, Udotea, Halimeda and probably some few others. 

 Together with the Algae a seagrass formation composed of the 

 genera Thalassia, Cymodocea, Halophila and Halodule is found, 

 of a similar character as the Zostera vegetation with us on loose 

 bottom, but this we shall not consider here. 



1 ) The Gharaceæ excepted. 



