392 THE MICROSCOPIST. 



out ; form variable, gelatinous or mucous, coriaceous, soft 

 or hard, elastic, slimy, containing simple, curved, and en- 

 tangled moniliform colorless or greenish filaments, com- 

 posed of cells, which seem solid, imbedded in amorphous 

 gelatinous matrix ; heterocysts globose, interstitial, larger 

 than ordinary joints of filaments. 



N. commune. N. cceruleum. N. verruconum. N. minat- 

 issimum. N. lichenoides. N. vesicarium. N. sphcericum. 

 N. pruniforme. N.foliacum. 



2. Monormia. Frond or phycoma definite, gelatinous, 

 elongated, linear; spirally curled and convoluted sheath, 

 inclosing a single moniliform filament ; heterocysts inter- 

 stitial ; sporanges from joints most distant from vesicular 

 cells. M. intricata. 



3. Anabaina. Filaments moniliform or cylindric, often 

 curled, in formless mucous matrix, often forming a float- 

 ing film, with vesicular cells (heterocysts) and sporangial 

 cells. 



* Without a membranous sheath. 



a. Trichormus. Heterocysts interstitial and terminal ; 

 sporanges first from cells most distant from heterocysts. 



b. Sphazrozyga. Heterocysts interstitial ; sporanges 

 from nearest cells. 



c. Cylindrospermum. Heterocysts terminal ; sporanges 

 as last. 



d. Dolichospermum. Heterocysts interstitial ; sporanges 

 indefinite and unequal. 



* * Filaments not included in membranous sheath. 



e. Aphanizomenon. Heterocysts none (?) ; sporanges 

 usually simple and unequal. 



f. Sperm.osira. Heterocysts interstitial, single or in 

 pairs ; sporanges as in Trichormus. 



10. ULVACE^E. Marine or fresh-water Algse, membra- 

 nous, flat, and expanded ; tubular or saccate fronds, com- 

 posed of polygonal cells firmly conjoined by their sides ; 



