140 



regard to its anatomical structure, but it differs from this alga by its 

 hypothallic filaments, running in little flabelliform groups over the 

 substratum; the colour of both alga3 is also different, P. Boergesenii 

 being of a dark purple colour with a greenish hue over it, P. Harvey- 

 ana of a bright red colour. Lastly P. Boergesenii is also character- 

 ized by the distinct veins running from the centre towards the 

 periphery. 



Found in shallow water, St. Croix, White Bay. (N. 1537 n, 1546 n, 

 1585 ii). Rust of Twist (N. 1442). In alcohol and dry specimens. 



4. Peyssonnelia (Cruoriella) Nordstedtii nov. spec. 



Thallus tota superficie inferiore adhaerens, paulum calcarius, 

 colore ignota, diametro usque ad 4 centimetrum, constans hypo- 

 thallo et perithallo. Hypothallus constat filis repentibus, juxtap- 

 positis, parva flabella efficientibus. Cellula apicalis filorum alta 

 et brevis, in sectione longitudinali altior filis hypothalli. 



Cellule long* 28 36 40 p, latse 16 20 28 , et 28 // altse. 



Perithallus constat filis adscendentibus, stratum satis crassum, 

 denique fissum formantibus. Pars inferior hujus strati perit, pars 

 superior hypothallum novum efficit, cum radiculus uni- et pluri- 

 cellularibus partem inferiorem tegente, radiculis iis in partem in- 

 feriorem penetrantibus. 



Cellulse altse 122036 u, latse 121620^. Nemathecia 

 cum tetrasporis quadripartitis, cruciatis, tantum immatura visa. 



Peyssonnelia (Cruoriella) Nordstedtii 1 ) resembles an alga col- 

 lected at the island of Nias, Sumatra^ that I have called in my 

 manuscript of the Siboga-algse, later on to be published, P. Nord- 

 stedtii. Both algse have in common a frond of soft texture, only 

 slightly incrustated with carbonate of lime and the peculiar way 

 of renovating the frond. 



P. Nordstedtii belongs to the subgenus Cruoriella on account of 

 its hypothallus consisting of filaments branching by repeated dicho- 

 tomy, which branches grow until other filaments, crossing their way, 

 stop their growth. The branching filaments form little elongated 

 fan-shaped groups, springing from a principal axis with larger 

 cells than the cells in the fan-shaped groups, just like what we 

 have seen in P. Boergesenii (Fig. 143). 



Characteristic of P. Nordstedtii is the way in which the peri- 



1 ) Named in honour of and in gratitude to Prof. O. NORDSTEDT at Lund, 

 the learned algologist, to whom I owe so many graceful acts of kind- 

 ness. 



