MARINE AI.GAE FROM EASTER ISLAND 



285 



Thallus adhering firmly to the substratum ± 300 »j. thick, consisting of a 

 mesothallus and a perithallus superior and inferior. Mesothallus consisting of 

 rlabella-like branched filaments. Perithallus superior consisting of oblique fila- 

 ments in the basal part, ending in a pretty broad straight upper part. 



Perithallus inferior having only oblique filaments, many of these running 

 out in rhizoids. 



Cells of perithallus superior ± 3 — 6 [J. broad and 8 — 9 [j. high. Cells of 

 perithallus inferior 5 — 9 ;j. broad and 18 [j. high. 



Organs of fructification not observed. 



As long as the organs of fructification are unknown it will remain doubtful 

 whether an alga, with a midlayer of cells giving off ascending and descending 

 filaments, is a representative of the genus EtJiclia (the type of which is E. Eos- 

 liei) or a representative of the genera Cruoriella or Peyssonnelia and differing 

 from the types of these genera no more than Ralfsia dcusta differs from Ralfsia 

 clavata} Ethelia Fosliei has a mesothallus with an extremely well defined 

 perithallus superior and inferior and nemathecia with paraphyses that have top- 

 cells adhering together and covering almost the tetrasporangium in a young 

 state. The new alga from Easter Island does not give any light on this matter 

 as none of my many slides showed signs of fructification. Its anatomical 

 structure mostly resembles EtJiclia (Peyssonnelia) biradiata from the Indian Ocean. 

 It differs from this alga by its mode of growth, for E. pacifica adheres firmly 

 to the substratum whereas E. biradiata may be very easily detached and seems 

 even here and there to lie loose on the substratum while growing. The thallus 

 of E. pacifica adheres so firmly that I found it impossible to make a good 

 slide through the thallus, unless I cut the substratum at the same time. The 

 decalcifying of the substratum, consisting mostly of worm tubes, required much 

 time as the tubes were of different consistence. The use of various acids had also a 

 destructive influence on the contents of the cells and propitiated the swelling of the 

 membranes, circumstances that were unfavourable to the making of good slides. 



Another difference between the two algae lies in the size of the filaments. 

 The ascending filaments of E. biradiata are ± 8 [i broad and are 2 — 3 times 

 as high as broad. Those of E. pacifica are broad 3 — 6 u. and 8 — 9 {j. high. 

 The filaments of the perithallus inferior are in both algae longer and broader 

 than the ascending filaments. The colour was gone in the specimens of E. 

 pacifica that I had for examination. E. biradiata has a bright red colour. 



Area of distribution: Endemic. 



Fam. Corallinaceae. 



Melobesieae, par Mme PAUL LEMOINE. 



M. SKOTTSBERG a recueilli quelques especes interessantes dans cette ile 

 isolee d'ou jusqu'ici non ne connaissait que deux especes: Porolithon onkodes 

 (Heyd.) Fosl. et Porolithon praetextatum Fosl.; il a d'ailleurs retrouve la premiere 

 de ces deux especes, associee a d'autres especes pacifiques littorales. 



1 conf. Reinke, Algenflora der Westl. Ostsee deutschen Anteils, 1889, p. 48. 



