74 TUFTS COLLEGE STUDIES, VOL. IV, No. 7 



Page 290, after generic account of GONGROSIRA, add, 



KEY TO THE SPECIES OF GONGROSIRA. 



I. Cells 6-14 M diam. ; branches of basal layer often penetrating sub- 

 stratum. I. G. /atus/n*. 

 i. Cells 15-30 M diam. ; no descending branches from basal layer. 



2. G. Debaryana. 



i. G. LACUSTRIS Brand, 1907, p. 502; Trauseau, 1917, p. 

 230. Fronds small, nearly flat, later confluent, dull green ; 

 base of procumbent filaments 6-14 p diam., usually about n /*, 

 erect branches of about the same size, short, little branched ; 

 cells varying, some short and with rich contents, of irregular 

 form, some longer, cylindrical and nearly empty. Reproduc- 

 tion by akinetes, and probably also by zoospores. Growing on 

 decaying wood and on stones ; in the former case the prostrate 

 filaments may send down branches penetrating the substratum. 

 Mich., Transeau. 



Page 294, for Key to the species of Microthanmion, substitute, 



i. Filaments 1-2.6 M diam. ; little branched. 3. M.exiguuin. 



i. Filaments 2.5-4 M diam. ; much branched, 2. 



2. Ramiiicaiiou dense; main stem and branches indistinguishable. 



i. M. Kuetzingianum. 

 2. Ramification open ; main stem distinguishable. 



2. M, strictissimtim. 



Page 295, after M. STRICTISSIMUM var. MACROCYSTIS, add, 



M. sxir.uuM Reinsch, 1877, p. 245; Transeau, 1917, p. 230. 

 Filaments 1. 1-2. 6 /* diam., sparingly branched, branches erect, 

 with few or noramuli, apices slightly clavate. Mich., Transeau. 



/ ';/, ,/ 



Much smaller than our other species. 



Page 297 and p. 90 of supplement, for Key to the Species of 

 Stigeocloniuni. substitute, 

 i. Erect filaments unbranched except at the extreme bate. 



S. subsimple.i-. 

 i. Brect filaments more or less densely branched throughout. a. 



2. Opposite branching predominant. 3. 



a. Alternate branching predominant. 9. 



3. Main filaments medium, or leas. 6. 5. tenuf. 



3. Main filaments 1 1-30 M diam. 4. 



4. Lower cells much inflated. 5. S. ventricosum. 



4' Lower cells slightly or not inflated. 5. 



5. Lower cells not over 2 diam. long. 6. 



5. Lower cells 2-8 diam. long. 7. 



