OSCILLATORIACEiE. 293 



This species is very common, and grows at all seasons 

 on rocks and sea-weeds, between the tide-marks. 



Rivxdaria nitida. The shining Rivularia. 



Fronds of a shining, bluish-green colour and irregular 

 shape, from half an inch to an inch or more in diameter, 

 gelatinously leathery, wrinkled, at first flat and solid, then 

 more or less globose and hollow, growing in confluent 

 groups ; threads tapering to a very fine point, arranged in 

 a somewhat dichotomous manner; those in the centre of 

 the frond distant from each other, those at the surface 

 closely packed. 



This is the largest and most conspicuous marine spe- 

 cies of British Rivularice. It grows on bare exposed 

 rocks between the tide-marks, during summer and au- 

 tumn, and is annual. It is common on the south coast, 

 in Ireland, and in the Channel Islands. 



Genus CXXVII. ACTINOTHRIX. 



" Frond stellate ; filaments elongate, subcylindrical, rather 

 flaccid, radiating from a free central mass; when young 

 this mass is large and spherical, and the fibres are short 

 and conical, giving the whole plant the appearance of a 

 CaWhrops. As the algaB grow the filaments gradually elon- 

 gate, become more cylindrical, that is, less conical and 

 tapering, and the central mass decreases in size until, in 

 the perfect plant, the long filaments seem to spring from 

 a central dot ; the endochrome is annulated, the rings nu- 

 merous and very narrow, looking as a series of coins ar- 

 ranged closely side by side would appear if placed within 

 a glass tube." (Dr. J. E. Gray, ' Journal of Botany,' n. 

 xxiv.) — Actesotheix, from the Greek aktis, a ray, and 

 thrix, hair. 



