OSCILLATORIACEiE. 
107 
Plate XLYIII. 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. XLYIII. D.) 
Hab. On mudflats, near highwater 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, it 
is seen to be simple and filiform below, but gradually increasing in diameter upwards 
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 XLYIII. D. Fig. 1. Stratified tufts of Calothrix dura, the natural size. 
Fig. 2. Portions of the filaments magnified. Fig. 3. Apex of a filament, more highly 
magnified. 
Y. 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 
