OSCILLATORIACE^. 109 



which the full grown frond assumes. The species are found either in the sea or in fresh 

 or brackish water, and even on damp soil. A terrestrial species is common in Europe 

 by the borders of clayey highways and paths, and may also be found in America. 



1. MiCROCOLEUS corymbosus, Harv.; fronds erect, rigid, tufted, multifid, the branches 

 erect, level-topped, linear-clavate, closed at the extremity ; filaments densely packed, 

 not oscillating. (Tab. XLVIII. B.) 



Hab. On mud-flats, near high-water mark, at Key West, mixed with Calothrix dura. 

 W.H.H. (v. V.) 



Fronds half sunk in the mud, erect, tufted, from an eighth to a quarter of an inch in 

 length, flexuous, tapering much to the base, gradually increasing in diameter upwards 

 and dividing above into three or four or more erect branches, the lowest of which are 

 longest, the upper gradually shorter, so that the apices of all are nearly on a level. 

 These apices are obtuse, and closed. The investing sheath is tough and firmly mem- 

 branous, and the enclosed filaments strongly cohere together, and are with difficulty 

 separated. The colour of the sheath is ochraceous yellow, and of the endochrome dull green. 

 The substance is very firm and rigid, and in drying the plant does not adhere to paper. 



Plate XLVIII. B. Fig. 1. Tufts of Mickocoleus corymbosus^ the natural size. 

 Fig. 2. Magnified view of two fronds. Fig. 3. Portions of the enclosed filaments, more 

 highly magnified. 



VII. RIVULARIA, Roth. 



Frond globose or lobed, fleshy, firm, composed of continuous radiating filaments, 

 annulated within ; each springing from a spherical globule. (In the sea or in fresh 

 water.) 



A fresh water species resembling the British R. pisum has been sent to me by Mr- 

 Eavenel from the Santee Canal, where it grows on submerged leaves and stems of plants. 

 It is hemispherical, very convex, dark blackish-green and soft, and consists of densely 

 set, spuriously branching, slender filaments. The specimens are not in a very perfect 

 state, and I cannot say to which, if any, of the modern species they would belong. In 

 old times they would pass for R. pisum, but it is nearly impossible at present to say 

 exactly what that species is. 



