F. Borgesen: Rhodophyceæ of the Danish W. Indies. 143 



Cellulæ longæ 20—28—32—40/7, latæ 16—20//, in sectione 

 altæ 20—24//. 



Perithalli cellulæ infimæ omnes fere æque altæ ae cellulæ 

 hypothalli ; in sectione transversali altiores quam latæ, in sectione 

 longitudinali fere quadraticæ, cellulæ superiores gradatim de- 

 crescentes. 



Cellulæ altæ 24— 28 /i, latæ 20^. 



Nemathecia in thallo parvas maculas obscuras irreguläres ef- 

 ficiunt, carposporis tripartitis zonatis et paraphysibus obtusatis 

 quorum cellulæ IV2 altiores sunt quam latæ. 



Nemathecia alta 200 fj.. Carposporæ 100 /i. Nemathecia cum 

 tetrasporangiis, cruciatim divisis. Tetrasporæ altæ 60 — 80^. 



Peyssonnelia simulans has received its name because it has 

 so many points in common with P. conchicola that I felt doubtful, 

 whether it might not be a form of P. conchicola but it can not 

 be identified with this alga and therefore I prefer to describe it 

 as a new species. 



P. simulans distinguishes itself from P. conchicola by adhering 

 loosely to the substratum; the collection of Dr. Børgesen con- 

 tains entire loosened specimens, whereas P. conchicola adheres 

 firmly to the substratum. The colour is different in both algæ, 

 P. simulans being of a bright pink colour — not red — and P. 

 conchicola of a red colour that fades partially away in drying. 

 The faded parts have a yellowish pink colour. 



It is true that as a rule colour is a bad characteristic of 

 algæ but in the Peyssonnelia it is such a marked feature, that 

 it probably can be of great help in knowing the different species. 



P. simulans resembles P. conchicola by its hypothallus con- 

 sisting of straight-running filaments ending in a short, high apical 

 cell, which is higher than the filaments are at a little distance 

 from the top. Its perithallus is characterized by an almost square 

 lower cell, that divides at its top, seen in longitudinal section, 

 in two rows of cells (Fig. 140). This is often the case in species 

 of Peyssonnelia but seldom so regularly and in such a marked 

 way as in this species. Under slight pressure on the covei: slip, 

 the cellrows loosen in vertical direction after decalcification and 

 this I have never observed in sections of P. conchicola. I could 

 study this alga thoroughly thanks to the kindness of Dr. A. Forti, 

 who send me an authentic specimen of Dr. Piccone for compari- 

 son. I may well thank him here for his kindness. 



The thallus of P. simulans is incrustated with carbonate of 

 lime; it is thin, the thickest thallus in Dr. Børgesen's collection 



