108 



forms are easily separated, each having the characters of the 

 respective typical forms. 



Quite in the same way as var. platydisca, var. platyloba is a 

 deep-water form occurring at the Danish Isles in depths from 

 10—20 fathoms. 



It is found in the sea round St. Jan. Off Cruz Bay and off America 

 Hill. It was growing partly on shells and stones, partly also upon the 

 loose bottom itself. 



Geogr. Distrib. Found in most warm seas. 



3. Halimeda Opuutia (L.) Lamx. 



Lamouroux, 1. c, p. 186. Barton, 1. c. p. 18. Borgesen, 1. c. p. 136. 



var. typica Barton, 1. c. p. 20. 



var. triloba (Decsne.) Barton, 1. c. p. 20. 



H. Opuntia occurs most often in shallow water, but once I 

 have found it in deeper water in about 10 fathoms ; it occurs both 

 on sheltered and on more exposed coast, var. triloba being a more 

 sheltered form, var. typica also occurring on more open coast ; it 

 is often found in the lagoons lying like large cakes loose upon the 

 bottom. 



It is a very common species, found everywhere with the 

 exception of the most exposed localities only. 



Geogr. Distrib. In all tropic oceans. 



4. Halimeda gracilis Harv. 



Harvey, Alg. Ceylon, No. 72. Barton, The genus Halimeda, p. 22. 



Of this nice species I have found a form in rather deep water 

 at St. Jan, which I think may be considered as new and for which 

 I have proposed the name : 



var. opuntioides Borgs., Fig. 87. 



Joints large, broadly suboval — reniform often distinctly cre- 

 nulated at the upper margin or sometimes even trilobed, having 

 upon the whole a very great resemblance to forms of Halimeda 

 Opuntia. The dried specimen is whitish-green in colour. The 

 joints are rather thick but easily breakable, the calcification 

 being not very strong. 



Joints up to 14 mm broad and 9 mm high. 



Whilst its outer appearance is in this way rather different 

 from the two forms (f. typica and f. laxa) we find figured in Mrs. 



