448 



slightly ramified or not at all, while in Acrochsetium cssspitiformis 

 the ramification is considerable; further, the sporangia in Acr. 

 gracile, owing to the scanty ramification, are placed up along 



the main filaments, while in Acr. csespitiforme 

 they are found at the base of the branches. 

 The plant was gathered at the end of 

 February in shallow water near the shore. 

 St. Croix: Salt River. 



12. Acrochsetium globosum Bergs. 



13. Sancti Thoinae Bergs. 



14. seriatum Bergs. 



15. flexuosum Vickers. 



16. Acrochaetiuin spec. 



Upon a young Padina Howeana a few 

 plants of an Acrochsetium were found, show- 

 ing apparently some likeness to Acr. flexuo- 

 sum. Having had so little material of it at 

 my disposal, I prefer to leave it unnamed. 



It forms tufts up to more than one 

 mm.; one specimens was about 1200// high. 



The base consists of short, creeping 

 filaments (Fig. 417 a); these are irregularly 

 bent, in the middle of the basal layer inter- 

 woven and merging together, but with free 

 ends. The cells in the basal filaments are 

 about 8 fj. thick and 11 fj. long. 



The erect filaments (Fig. 417 b) arising 

 from the basal filaments are from 10 13 fj. 

 thick and the cells about 35 n long. Upwards 

 the main filaments do not taper much : until 

 at about 8 11 //. 



The filaments are very ramified; from 

 near the base they carry branches given 

 off irregularly at all sides with longer and 

 shorter rows of bare cells in between, and often with some ten- 

 dency to secund arangement. The branches are given off at 

 acute angles; they seremto be rather rigid and are a little curved. 

 They are somewhat thinner than the main filaments, at their 

 base about 9 /^, tapering to -about 5 to 6 p. at their apex. 



Fig. 417. Acrochsetium 

 spec, a, base of the 

 plant, b, part of erect 

 filament. (a, about 

 200:1; b, about 150:1). 



