Myxophyceae 271 



very often to the sheaths of the older filaments and resemble branches very 

 strongly indeed. Intercalary heterocysts do occur in C. p a r i e t i n a, 

 but they are not at all common. The species is usually readily distin- 

 guished by its lamellose, brown and more or less ochreate sheath, but these 

 characters may be at times more or less obscure." — Setchell. 



489. Calothrix castellii (A. Massalongo) Bornet and Flahault. Revis. des 



Nostoc. Ann. Sci. Nat. Bot. VII. 3: 369. 1886. De Toni. Syll. Algar. 

 S: 627. 1907. 



WoUe. Fresh-Water Algae U. S. 255. pi. 182. f. 8-10; pi. 184. f. 35, 38-40; 

 187. f. 3-33. (Scytonema castellii Mass.) ; 262. pi. 189. f. i. 1887. 



Plant mass spongy, cushion-shaped, widely expanded, the surface 

 pubescent or hirsute by the projecting ends of the filaments, dull blue- 

 green; filaments 12-13 ™ic. in diameter, 4-8 mm. in length, curved, flex- 

 uous, densely crowded, sometimes agglutinated, erect, decumbent and 

 bulbous at the base; sheaths thin, close, firm, uniform, transparent or yel- 

 lowish; trichomes 8-10 mic. in diameter, tapering into a very long hair; 

 cells two to four times shorter than their diameter; heterocysts basal. 



Pennsylvania. On shelves, walls and flower pots in greenhouse. Harris- 

 burg. (Wolle). 



490. Calothrix donnellii (Wolle) De Toni. Syll. Algar. 5: 629. 1907. Wolle. 



Fresh Water Algae. Bull. Torr. Bot. Club. 6: 283. 1879. (M a s- 



tigonema donnellii Wolle). 

 Plant mass caespitose, mucous, olivaceous; filaments 6-12 mic. in 

 diameter, at the base sometimes 15-20 mic. in diameter, simple or branched, 

 flagelliform; very gradually tapering, sometimes thin and flaccid, sometimes 

 strong and rigid, slightly curved, densely interwoven; sheaths very thin, 

 colorless, at first drawn out into a hair, afterwards often truncate and open; 

 trichomes frequently interrupted; cells usually four or five times shorter 

 than their diameter; transverse walls distinct; heterocysts basal, rarely 

 intercalary; cell contents pale or bright blue-green, sometimes brownish. 

 Pennsylvania? On wood in salt water, submerged. (Wolle). 



491. Mastigonema elongatum Wood. Contr. Hist. Fresh-Water Algae 



North America. 53. pi. 5. f. i. 1872. Wolle. Fresh-Water Algae U. 

 S. 243. pi. 174. f. 9. 1887. De Toni. Syll. Algar. 5: 631. 1907. 



Plant mass at first somewhat spherical, afterwards frequently spindle- 

 shaped, slippery, firm, blackish green; filaments up to 6 mic. in diameter, 

 very elongate, sometimes truncate at the apex, but generally produced into 

 a long, flexuous, translucent hair; sheaths close, transparent, frequently 

 truncate at the apex; trichomes sometimes strongly constricted at joints; 

 cells short; transverse walls sometimes not visible; heterocysts somewhat 

 spherical. 



Pennsylvania. On brook moss in an aquarium. (Wood). 



492. Mastigonema fertile Wood. Contr. Hist. Fresh-Water Algae North 



America. 54. pi. 5. f. 3. 1872. Wolle. Fresh-Water Algae U. S. 244. 

 1887. De Toni. Syll. Algar. 5: 630. 1907. 



