192 



divided by vertical and horizontal walls into smaller, more or 

 less cubical cells. The sporangia are about 5 — 6// thick. 



So far as I can see, this form seems to be very nearly re- 

 lated to Ralfsia verrucosa and especially it comes near to that 

 large form collected by Schousboe in Maroc and described by 

 KucKUCK in "Bemerkungen zur marinen Algenvegetation von 

 Helgoland", I, p. 244, The most essential differences between 

 the West Indian form and Ralfsia verrucosa are, that the spor- 

 angia in the first-mentioned form seem to be somewhat longer 

 sometimes nearly clavate, that the sporangia have a small cell 

 at their base, which is not mentioned in Kuckuck's description 

 nor found in the excellent figures of Ralfsia verrucosa in Reinke's 

 "Atlas"; only in Harvey, "Phycologia Britannica", pi, XCVIII, 

 fig, 5 such a cell is figured. As to the plurilocular sporangia a 

 difference is also present, the large top cell of the sporangia in 

 Ralfsia verrucosa being after Kuckuck, 1, c, p, 242, colourless and 

 sterile. On the other hand, the paraphyses of the West Indian 

 form seem quite to agree with those of Ralfsia verrucosa. 



So long as our knowledge of Ralfsia verrucosa and its diffe- 

 rent forms remains somewhat deficient (cfr, Reinke, 1. c, and 

 Kuckuck, 1. c) I think it most correct to consider our form as a 

 special species. Should later examinations of the different forms 

 now referred to Ralfsia verrucosa show, that they all really belong to 

 this species, it would perhaps be most natural to consider the 

 West Indian form also as a variety of R. verrucosa. 



This species occurred in shallow water near the surface of 

 the sea on rocks and stones in rather exposed as well as more 

 sheltered localities. It is found with unilocular and plurilocular 

 sporangia in the months December — March, 



It is a common species at the shores of the Danish Islands, especially 

 at St. Thomas and St. Jan. 



Geogr. Distrib. West Indies, Indian Ocean. 



Fain. 6. Lithoderfnatacefe. 

 Lithoderma Aresdi, 



1. Lithoderma spec. 

 Upon a stone together with Ralfsia were found some thin 

 crusts of a brown alga. It has marginal growth and consists of 

 a basal layer of cells from which the erect filaments grow up- 

 wards (Fig, 149), 



