624 SCYTONEMATACEAE. 



2. Schizothrix chalybea Gomont, Monogr. 57. pi. 9. f. 3-5. 1893. 



On mud, in company with Scytonema velutinum, New Providence. Type locality 

 Mexico : no other records. The determination is from the description, as type ma- 

 terial is at present inaccessible. 



Family 4. NOSTOCACEAE. 



1. NOSTOC Vaueher, ex Born. & Flah. Ann. Sci. Nat. Bot. VII. 7: 1S1. 1888. 



1. Nostoc commune Vaueher, ex Born. & Flah. Ann. Sci. Nat. Bot. VII. 7: 



203. 1888. 



New Providence, Castle Island, and Crooked Island : universally distributed in 

 warm and temperate regions, on ground and rocks. Type from Switzerland. 



2. HORMOTHA'MNION Grunow, ex Born. & Flah. Ann. Sci. Nat, Bot. VII. 



7: 259. 1888. 



1. Hormothamnion enteromorphoides Grunow, ex Born. & Flah. loc. cit. 260. 



1888. 



North Cat Cay, Caicos Islands, and Watling's Island : generally distributed in 

 tropical and subtropical waters. Type from Guadeloupe. 



Family 5. SCYTONEMATACEAE. 



1. SCYTONEMA Ag. ex Born. & Flah. Ann. Sci. Nat. Bot. VII. 5: 



85. 1887. 



1. Sheaths homogeneous or with uniform parallel strata. 2. 



1. Sheaths with plainly divergent strata. 5. 



2. Aquatic : sheaths firmly membranaceous. 1. S. cincinnatum. 



2. Terrestrial. 3. 



3. Heterocysts compressed, shorter than the diameter of the tri- 



chome. 2. /S. MiUei. 

 3. Heterocysts quadrate or longer. 4. 



4. Filaments mostly prostrate, 10 18 w in diameter. 3. 8. oceJlatnm. 



4. Filaments in erect fascicles, usually 7 12 in diameter. 4. 8. Hofmanni. 



5. Strata of sheath moderately divergent, rather firm. 5. S.myochrous. 

 5. Strata of sheath strongly divergent, gelatinous and diffluent. 6. 



6. Cells and heterocysts shorter than the diameter of filament. 0. S. velutinum. 



6. Cells quadrate or longer ; heterocysts quadrate or globose. 7. S. crassum. 



1. Scytonema cincinnatum Thuret, ex Born. & Flah. Ann. Sci. Bot. VII. 5: 



89. 1887. 



New Providence and Bimini : widely distributed. Type from Germany. 



2. Scytonema Millei Born. & Flah. Ann. Sci. Nat, Bot. VII. 5: 93. 1887. 



New Providence, Berry Islands, South Cat Cay, and Watling's Island : North 

 and South America. Type from Guiana. 



3. Scytonema ocellatum Lyngb. ex Born. & Flah. Ann. Sci. Nat. Bot. VII. 5 : 



95. 1887. 



New Providence : widely distributed. Type from Denmark. 



4. Scytonema Hofmanni Ag. ex Born. & Flah. Ann. Sci. Nat. Bot. VII. 5: 



97. 1887. 



New Providence, Abaco, and Acklin Island : widely distributed. Type from 

 Sweden. 



