OSCILLATORIACEtE. 107 



Plate XLVIII. C. Fig 1. Stratified tufts of Calothrix pilosa, the natural size. 

 Fig. 2. Portion of the filaments magnified. Fig. 3. A more highly magnified portion. 



5. Calothrix dura, Harv. ; strata indefinite, dull brown ; filaments at first decum- 

 bent and matted together, then erect, cohering laterally in tooth-like bundles ; each 

 filament angularly bent below, at first simple, then cleft longitudinally and afterwards 

 once or twice forked ; endochrome very narrow, annulate ; the cell-wall thick, lamel- 

 lated and subopaque ; apices acuminate. (Tab. XLVIII. D.) 



Hab. On mudflats, near high water mark. Key West, W. H. H. (v. v.) 



Possibly this may be only a state of the preceding species, to which, at least, it is 

 nearly allied, although it offers characters which would cause it to be referred to another 

 genus of Kiitzing. The filaments are matted together at base ; the mat being composed 

 of prostrate portions of each thread, intricately interwoven. The threads, after proceeding 

 for a time horizontally, suddenly become erect, bending nearly at right angles, and then 

 they cohere together into stiff", tooth-like fascicles, in which they stand parallel, and are 

 straight or but slightly curved. When a single filament is removed from the fascicle, i 

 is seen to be simple and filiform below, but gradually increasing in diameter upwardi 

 to a certain stage, at which the endochrome separates into two columns, which are at 

 first parallel with each other and contained in the same sheath ; but they soon separate, 

 and then each becomes invested by a separate sheath. In this way two branches are 

 formed, which may either remain simple or may again divide once or twice in a similar 

 manner. The cell-wall is much wider than the endochrome. The substance is rigid 

 and tough : and the colour dull brown or fulvous. 



Plate XLVIII. D. Fig. I. Stratified tufts of Calothrix c?Mm, the natural size. 

 Fig. 2. Portions of the filaments magnified. Fig. 3. Apex of a filament, more highly 

 magnified. 



V. OSCILLATORIA. Vauch. 



Filaments lying in a gelatinous matrix, rigid, simple, acicular, vividly oscillating. 

 Tube continuous ; endochrome green, densely annulated with close, parallel, trans- 

 verse striae. (Mostly in fresh water — some marine.) 



The Oscillatorice occur in gelatinous strata or pellicles, which at first are formed at 

 the bottom of stagnant or running water, and afterwards rise to the surface. The green 

 scum frequently seen on the surface of putrid ditches is generally formed by one or 



