212 CORALS 



Mediterranean Sea, but is also found in shallow water in 

 many parts of the Tropics. Being a green plant and there- 

 fore dependent upon direct sunlight, as are all the Algae, 

 it cannot live in very deep water. Gardiner found it alive 

 at a depth of 55 fathoms in the Indian Ocean — not far 

 from the extreme limit of its bathymetrical distribution ; 

 but as it is comparatively light in texture and easily broken 

 up by wave action, the dead fragments and isolated joints 

 are frequently washed away into deep water and form there 

 an important constituent of the sea-bottom. Thus Darwin ^ 

 states that, off Keeling Island, at a greater depth than 

 90 fathoms the bottom was thickly strewed with joints of 

 Halimeda. 



But it is in the shallow waters of the lagoons, or among 

 branches of coral on the reefs protected from the rough 

 and tumble of the breakers, that Halimeda principally 

 flourishes and adds its quota to the calcareous deposits 

 of the tropical seas. 



Two other genera of calcareous Algae belonging to the 

 same family may be mentioned. 



Penicillus is a beautiful little coralline Alga from one 

 to four inches in height consisting of a cylindrical stem, 

 attached below to the mud and sand in which it grows by 

 a fibrous root mass, and terminating in a brush-like tuft 

 of free filaments. The shape of this plant has led to the 

 popular name for it of " the Merman's shaving brush." The 

 genus seems to be widely distributed in the tropical seas, 

 but very common in certain localities in the West Indies. 



Tydemannia has only recently been described from 

 shallow water in the Malay Archipelago and Indian Ocean. 

 It is a remarkably interesting little form consisting of a 

 moniliform stem and branches, dividing up into a complex of 

 twisted tufts or groups of fan-shaped branchlets terminating 

 in long cylindrical filaments.^ 



' C. Darwin, Coral Reefs, p. 117. 



- For further information on these genera and other calcareous 

 Codiaceae see A. and E. Gepp, Codiaceae of the Sihoga Expedition, livr. Ivi., 

 1911. 



