F. Børgesen: Phæophyceæ of the Danish \Y. Indies. 33 



The size of the cells differs rather much, their length being 

 about 20 n and their breadth 10 ii more or less. 



Near the periphery the disc consists of a single layer of cells, 

 in the middle of several. From the surface long hairs and short 

 assimilating filaments grow upwards. The hairs have a basal 

 growth zone and long colourless cells at their top. They have 

 a well-developed sheath at their base. 



Their diameter is about 14 p. 



The assimilating filaments consist of 2 — 3 cells and reach a 

 height of about- 35 j«; the cells contain some irregularly shaped 

 small chromatophores. 



In the middle of the disc the cells in the upper end of the 

 assimilating filaments were divided by longitudinal walls being at 

 the same time also darker coloured, this most probably being 

 the beginning of the plurilocular sporangia. Above these divided 

 cells the epidermis of the mother cell was often present in the 

 mucilage. No further developed sporangia were found and a 

 more definite determination is therefore impossible. 



Only found once, St. Thomas: at the shore of Water Island. 



Fam. 5. Ralfsiacece. 



Ralfsia Berk. 



1. Ralfsia expansa J. Ag. 



J. Agardh, Species Algarum, I, p. 63. F. Borgesen, Two crusta- 

 ceous brown algæ from the Danish West Indies (Nuova Notarisia, Serie 

 XXIII, 1912). A. Weber, Algues du Siboga, I, p. 146. 



Myrionema (?) expansum J. Ag., Nya alger från Mexico (Öf versigt af 

 K. Vetenskaps-Akademiens Forhandlinger, 4, 1847, p. 5, Stockholm 1848). 



Though using the name of J. Agardh for this plant I may 

 point out that the description of Agardh (1. c.) is so poor that 

 an identification by means of it is impossible and as, moreover, 

 the original specimen of Ralfsia expansa, collected by Liebmann 

 at Vera Cruz and now in the Botanical Museum, Copenhagen, is 

 sterile, an exact identification by means of it is also excluded. 

 The using of Agardh's name in spite of this is chiefly because 

 the sterile thallus of Liebmann's specimen seems quite to agree 

 with my specimens and furthermore also, because the plant in 

 question has been found in nearly the same flora-district. 



The plant when young forms orbicular later on more irregu- 

 lar crusts, often growing together to coriaceous expansions on 



Dansk Botanisk Arkiv, Bd. 2. Nr. 2. 3 



