NO. 2 drouet: myxophyceae 23 



interior of the mass where few healthy trichomes are to be found; 

 on the surface, the sheaths are often definitely diffluent. More than 

 one trichome within a sheath are rarely observed. In careful dis- 

 sections of material preserved in formalin, the closed ends of the 

 sheaths may be seen. 



/. submersa, forma nov. 



Forma typica similis sed trato subsphaerico vel depresso-sphaerico, 

 submerso, gelatinoso; filamentis phormidioideis, vaginis totum dif- 

 fluentibus. 



Hab.: lapidibus in aquam subsalsam submersis affixa, MEXICO: 

 Oaxaca, tide pools, Tangola-Tangola Bay, No. 557, February 28- 

 March 1. {Type in U. S. National Herbarium). 



The specimen cited consists of filaments which exhibit the same 

 tortuous habit of growth encountered In the typical subaerlal S. Han- 

 cockii, but here the sheaths are always entirely diffluent into an 

 amorphous hyaline mucus which becomes bright blue when treated 

 with chlor-zinc-iodine. The trichomes are morphologically identical 

 with those of the type of S. Hancockii. I interpret the f. submersa as 

 an ecological form which can be distinguished taxonomically only 

 when the plant mass is produced beneath the surface of the water. 



Hydrocoleum comoides (Harvey) Gomont, Ann. Sci. nat. VII, 

 Bot. 15: 335. 1892. 



Forma trichomatlbus 15/i, ad 20/a crassis, ad genicula constrictis, 

 intra vaginam praecipue singulis, ad apices attenuatis et truncatis, 

 dissepimentis evidenter granulatis. Fig. 7. 



MEXICO: Revilla Gigedo Islands, abundant In certain tide 

 pools, Braithwalte Bay, Socorro Id., No. 22, January 2-4; high warm 

 tide pools, Sulphur Bay, Clarion Id., No. 65, January 5. ECUADOR: 

 Galapagos Islands, in higher tide pools, Wenman Id., No. 85, Jan- 

 uary 11. 



Our material Is somewhat reminiscent of Lyngbya aestuarii 

 (Liebm.) Gom., especially since most of the filaments contain single 

 trichomes. The trichomes are all distinctly constricted at the dis- 

 sepiments, however, and the sheaths are conspicuously mucous; here 

 and there a filament Is found containing more than one trichome, and 

 frequent false branching occurs. The material at hand exhibits the 

 characteristic form of the colony: caespltose mats bearing short 

 'erect glutinous tufts. 



