292 BRITISH SEA-WEEDS. 



Genus CXXV. SCHIZOSIPHON. 



Frond a globose or lobed gelatinous crust, composed of 

 closely packed, ringed, radiating, sheathed threads, each of 

 which springs from a transparent cell ; sheath gelatinously 

 membranous, cleft into numerous longitudinal fibres. — 

 Schizosiphon, from the Greek scliizo, to divide, and siphon, 

 a tube. 



Schizosiphon Warrenise. Miss Warren's 

 Schizosiphon. 



" Fastigiately branched, the lowest cell of the branches 

 wider, hemispherical, lateral ; sheaths dark-coloured, the 

 fibres often spiral; apices of the branches much attenua- 

 ted." — Caspar y. 



Genus CXXVI. RIVULARIA. 



Frond irregularly globose, fleshy, composed of continu- 

 ous, radiating threads, which are annulated within, and 

 have a transparent, spherical cell at the base. — Rivttlabia, 

 from the Latin rivulus, a small brook. 



Rivularia plicata. The wrinkled Rivularia. 



Fronds of a dark green colour and irregular shape, gela- 

 tinous, from one-tenth of an inch to half an inch in diame- 

 ter, wrinkled, hollow, often ruptured, growing in confluent 

 groups ; threads tapering gradually to a fine point, ar- 

 ranged in dichotomous series. 



Rivularia atra. The black Rivularia. 



Fronds of a glossy black colour, minute, globose, or 

 hemispherical, smooth, firm, growing singly; threads awl- 

 shaped, closely packed, of a dark green colour. 



