30 REPORT OF COMMISSIONER OF FISH AND FISHERIES. 



2. Filaments furnished with heterocysts 10 



Filaments destitute of heterocysts 3 



3. Filaments spirally twisted Spirulina. 



Filaments not twisted 4 



4. Filaments without a distinct sheath 5 



Filaments formed of one or more colored trichomata contained in a 



transparent sheath 6 



■ 5. Cells bluish green or purple Oscillaria. 



Cells colorless, or filled with minute black grains Beggiatoa. 



6. Sheath containing several trichomata Microcoleus. 



Sheath containing only one trichoma Lyngbya. 



7. Filaments free, forming tufts of indefinite extent Calothrix. 



Filaments united by a more or less firm gelatinous substance, 



frond of definite shape and extent 8 



8. Heterocysts basal, i. e., placed at the base of the principal filaments 



and branches 9 



Heterocysts intercalary Hormactis. 



9. Frond hemispherical or vesiculose, filaments radiating from the 



base Bivularia. 



Frond plane, filaments parallel Isactis. 



10. Filaments destitute of a sheath Sphcerozyga. 



Filaments consisting of a trichoma in a sheath Nodularia. 



SPH^EOZTGA, Ag. 



(From aipaipa, a sphere, and ^vyog, a yoke. ) 



Filaments free, destitute of sheath. Spores produced in the cells adja- 

 cent to the heterocysts. 



S. Carmichaelii, Harv., Phyc. Brit., PI. 113 a. (Cylindrospermum, 

 Kiitz., Spec. Alg., p. 294. — Andbaina marina, Breb.). PI. I, Fig. 3. 



Filaments flexuous, densely interlaced, forming slimy bluish-green 

 expansions, cells cylindro-spherical, about .0035 mm in diameter, dimin- 

 ishing in size towards the end of the filament, terminal cell pointed. 

 Heterocysts several in each filament. Spores oblong, usually one on 

 each side of heterocyst, about ,018 mm in length when ripe, rather more 

 than twice as long as broad, at first green, then yellowish. 



Noank, Conn.; Wood's Holl, Gloucester, Cambridge, Mass.; Europe. 

 Summer. 



Probably a common alga along our whole coast in midsummer and autumn on 

 decaying algj©, looking like a shining emerald-green film. It occurs most frequently 

 on the surface, but is also found at the depth of several feet. In his work on the 

 Fresh-water Algte of America, Prof. H. C. Wood, jr., mentions the present species as 

 occurring at Camden, N. J. We cannot, however, agree with him in placing it in 



