THE LITHOTHAMNIA OF THE MALDIVES AND LACCADIVES. 



By M. FosLiE, in Trondhjem. 



(With Plates XXIV and XXV.) 



The Lithothamnia of the tropics have been rather disregarded. Although for a long 

 time known as appearing in a gi-eat number of individuals, up to late years only a few 

 species of rather uncertain limits have been distinguished. This applies to the branching as 

 well as crust-like forms. The latter and in part the branching also have often been considered 

 to represent a solitary and supposed cosmopolitan species, Phymatolithon polymorphum {Litho- 

 thamnion polymorphum, auct.), while in reality this plant shows a rather restricted geographical 

 distribution, being properly known to occur only in some parts of the North Atlantic and 

 within the southern part of the Arctic Sea. In regard to species also the Lithothamnia 

 have now been shown to be richly represented in the tropics, as of late years rather numerous 

 species have been described. Little, however, is as yet known with regard to their geographical 

 and vertical distributions. Therefore, every contribution may help to extend our knowledge 

 of these plants, which appear to be significant and interesting in several respects. 



Till now not a single species with certainty has been recorded from the great area 

 between the Red Sea and the East Indies. Mr Stanley Gardiner, however, collected a number 

 of Lithothamnia during his expedition to the Maldives and Laccadives in 1899 — 1900. He 

 has done me the favour of submitting this collection to my research. It is interesting, 

 especially as regards the geographical distribution of several species, and at the same time 

 tends to show what forms chiefly act together with corals as reef-builders. 



The calcareous algae in question, in the northern temperate zone as well as in the 

 Arctic Sea, occur rather independently and, as a rule, form greater or smaller banks in the 

 sublittoral zone down to a depth of about 20 fathoms'. In the tropics these algae partly 

 seem to be confined to coral-reefs, and partly form independent banks, which mainly consist 

 of calcareous algae freely, or apparently freely, developed on the bottom. The gi-owth of 

 the species under different conditions, however, is still but little observed, as well as to what 

 extent banks, or masses, of these algae occurring on reefs consist of one or more species. 

 I may mention that banks in the tropics seem not unfrequently to be composed of a single 

 species, as is very often the case in the temperate zone. Thus the Challenger expedition 



1 F. E. Kjellman, "The Algae of the Arctic Sea." Lithothamnion." Trondhjem, 1895. 

 Stockholm, 1883. M. Foslie, "The Norwegian Forms of 



