OSCILLATORIA'CEAE. 623 



5. PLECTONEMA Thuret ex Gomont, Monogr. 116. 1893. 



Trichomes torulose ; filaments inhabiting colonies of gelatinous 



algae. 1. P. nostocorum. 



Trichomes not torulose ; filaments matted into a rose-colored 



membrane. 2. P. roseolum. 



1. Plectonema nostocorum Born, ex Gomont, Monogr. 122. pi. 1. f. 11. 1893. 



New Providence, in colonies of Gloeothece, etc. : common everywhere in similar 

 habitats. Type from France. 



2. Plectonema roseolum Gomont, Monogr. 122. pi. 1. f. 9-10. 1893. 



On sand and mud, New Providence : Europe ; North America. Type from 

 Germany. 



6. SYMPLOCA Kiitz. ex Gomont, Monogr. 124. 1893. 

 1. Symploca hydnoides forma fruticulosa Gomont, Monogr. 127. 1893. 



North Cat Cay and Great Bahama : the typical form is widely distributed, the 

 type from Great Britain ; no type locality for the forma fruticulosa which occurs 

 generally with the typical form. 



7. HYDROCOLEUM Kiitz. ex Gomont, Monogr. 71. 1893. 



Sheath cylindrical, distinct. 1. H. oomoides. 



Sheath irregular, often becoming shapeless and diffluent. 



Trichomes usually 9-1 1^ in diameter. 2. H.lyngbyaceum. 



Trichomes seldom under 17 # in diameter. 



Filaments forming tufts attached to algae or to sand 

 and rocks ; sheaths broad, with irregular and erose 



margins, but fairly persistent. 3. H. cantharidosmwrn. 



Filaments not attached, forming an indefinite gela- 

 t- tinous stratum ; sheaths very irregular or shape- 



less, soon diffluent. 4. H. glutinosum. 



1. Hydrocoleum comoides Gomont, Monogr. 73. pi. 12. f. 3-5. 1893. 



Great Bahama and Exuma Chain : Bermuda ; Guadeloupe ; Australia. Type 

 from Australia. 



2. Hydrocoleum lyngbyaceum Kiitz. ex Gomont, 75. pi. 12. f. 8-10. 1893. 



Caicos Islands and Great Ragged Islands : of general distribution. Type from 

 France. 



3. Hydrocoleum cantharidosmum Gomont, Monogr. 74. pi. 12. f. 6-7. 1893. 



Mariguana : widely distributed in warmer waters. Type from the Canary 

 Islands. 



4. Hydrocoleum glutindsum Gomont, Monogr. 77. 1893. 



Caicos Islands : 'Europe and America. Type from Sweden. 



The genus Hydrocoleum is fairly distinct from neighboring genera, but the spe- 

 cies have much similarity. Absolute certainty of determination can be obtained 

 only by observing the development of the living plant. 



8. SCHIZOTHRIX Kiitz. ex Gomont, Monogr. 30. 1893. 



Sheaths hyaline, trichomes 2-3 # in diameter. 1. S. vaginata. 



Sheaths with inner layer violet or slate color; outer layer hyaline, 



trichomes 7-9 /i in diameter. 2. S.chalybea. 



1. Schizothrix vaginata Gomont, Monogr. 40. pi. 7. f. 1-4. 1893. 



New Providence and Caicos Islands : generally distributed. Type from Switzer- 

 land. 



