Myxophyceae 207 



. 4 Filaments long, entangled, flexuous, much branched, forming a rose- 

 colored or reddish brown mass adhering to rocks or larger algae; 

 trichomes 1.2-2 mic. in diameter P. golenkinianum 



5 Filaments very long, entangled in dense balls; trichomes 2-2.5 mic. 



in diameter P. calothrichoides 



6 Filaments long, flexuous, much branched, forming a black or brown- 



ish green mass; trichomes 2-3.5 mic in diameter 



P. battersii 



381. Plectonema tenue Thuret. Essai Class. Nostochinees. Ann. Sci. Nat. 



Bot. VI. i: 380. 1875. Gomont. Monogr. Oscill. 121. pi. i. f. 5, 6. 



1893. De Toni. Syll. Algar. 5: 492. 1907. 

 Collins. Algae. Flora of the Blue Hills, Middlesex Fells, Stony Brook 

 and Beaver Brook Reservations of the Metropolitan Park Commission. 127. 

 1896. 



Plate XI, fig. I, 2. 



Plant mass caespitose, rotund, light green; filaments graceful, elongate, 

 much branched; false branches usually in pairs; sheaths at first colorless 

 and very thin, later becoming thick, and yellowish orange in color; trich- 

 omes 5-10 mic. in diameter, here and there constricted at joints, tapering 

 at the apex; apical cell tapering, obtuse conical; cells 2-6 mic. in length; 

 transverse walls not granulated; cell contents finely granular, pale blue- 

 green. 



Massachusetts. Spot Pond, Middlesex Fells. (Collins). 



382. Plectonema tomasinianum (Kuetzing) Bornet. Les Nostocacees he- 



terocystees du Systema Algarum de C. Agardh (1824) et leur 



Synonymie actuelle. (1889). Bull. Soc. Bot. de France. 36: 155. 1889. 



Gomont. Monogr. Oscill. 119. 1893.. De Toni. Syll. Algar. 5: 490. 



1907. 

 Wood. Contr. Hist. Fresh-Water Algae North America. 59. pi. 8. f. 6. 

 1872. (Scytonema nagelii (Kg.) Wood). Rabenhorst. Die Algen 

 Europas. no. 2493. 1877. (P. mirabile Thur.). Wolle. Fresh Water 

 Algae. Bull. Torr. Bot. Club. 6: 285. 1879. (Calothrix mirabilis 

 Ag.). Wittrock and Nordstedt. Algae Aq. Dulc. Exsicc. no. 391. 1880. 

 Wolle. Fresh Water Algae. VII. Bull. Torr. Bot. Club. 10: 20. 1883; Fresh- 

 Water Algae U. S. 266. pi. 181. f. 12-15. 1887. Bennett. Plants of Rhode 

 Island. 114. 1888. (Scytonema natans Breb.). Wolle and Martin- 

 dale. Algae. Britten's Catalogue of Plants found in New Jersey. Geol. Surv. 

 N. J. 2: 603. 1889. (Calothrix brebissonii Kg.). Snow. The 



Plankton Algae of Lake Erie. U. S. Fish Comm. Bull, for 1902. 22: 392. 

 1903- 



Plate XI. fig. 3. 



Plant mass caespitose, more or less expanded, brownish green or rarely 

 dull blue-green, up to 2 cm. in height; filaments entangled, flexible, usually 

 flexuous, repeatedly branched; false branches often in pairs, issuing in an 

 erect, spreading or oblique manner; sheaths at first thin, colorless, with age 



