390 THE MICROSCOPIST. 



18. Sirosiphon. Filaments single, double, or triple, in 

 distinct common sheath, articulated, branched by lateral 

 budding ; branches divergent. 



19. Sehizothrix. Filaments branched by division ; 

 sheaths lamellated, thick, rigid, curled, thickened below, 

 finally longitudinally divided. 



20. Sympkyosipkon. Filaments erect or ascending, in- 

 closed in lamellated hard sheaths, concreted laterally at 

 their bases, involved in jelly. 



21. Rhizonema. Sheath cellular, with branched and 

 anastomosing rootlets (?) ; filaments annulated, inter- 

 rupted here and there by a connecting cell ; branches in 

 pairs from protrusion of filament. 



D. RIVULARIE^E. Filaments articulated ; enlarged basal 

 cell, attenuated above, connected into definite or indefinite 

 fronds ; motionless. 



22. Schizosiphon. Basal cells globose; filaments simple, 

 sheathed; sheaths in groups, dark-colored, hard, open, 

 and expanded above, and overlapping so as to form a 

 succession of ochrese, which have the free borders slit up 

 into filaments or fringes; also displaying a spiral struc- 

 ture in dissolution. 



23 . Physactis. Filaments whip-shaped, torulose at base ; 

 sheaths simple, gelatinous, in a globose and solid, or sub- 

 sequently a bullose, vesicular frond ; in globose fronds 

 filaments radiate from centre, in vesicular from internal 

 (lower) surface of gelatinous matrix. 



24. Ainactis. Filaments branched, articulate ; thin 

 sheaths in solid pulvinate frond, which is concentrically 

 zoned by the dichotomous branching of filaments ; sheaths 

 more or less solidified by carbonate of lime ; sometimes a 

 spiral structure in dissolution. 



25. Rivularia. Filaments with an oval basal cell, suc- 

 ceeded by a cylindric manubrium, the remainder short, 

 attenuated upwards (whip-shaped) ; sheaths sometimes 



