374 Marine Algce of Berwlck-on-Tweed. 



66. Fronds nearly black, substance dense. ... ... ... 67 



Fronds rose-red or purple, rather succulent or gelatinous, sometimes 

 capillary. ... ... ... ... ... ... 69 



67. Fronds dichotomous, cylindrical, cartilaginous. ... ... 68 



Fronds pinnate or pinnatifid, compressed or cylindrical, cartilaginous, 

 purple or yellowish, tetraspores tripartite, immersed in the substance 

 of the frond, cystocarps external, sessile. ... ... Laurencia. 



Fronds filiform, rigid, wiry, irregularly branching, forming dense, 

 intricate bundles. ... ... ... ... Ahnfeltia. 



Fronds cylindrical or slightly compressed, cartilaginous, sparingly and 

 irregularly branching, composed of an inner layer of very large 

 angular colonrless cells, and a cortical layer of small coloured cells, 

 tetraspores cruciate immersed in the frond, cystocarps external, sessile. 



Oracilaria. 

 Fronds small, compressed, pinnate, forming small tufts, spores borne 

 on an axial placenta in the enlarged terminal branches. Gelidium. 



68. Root an expanded disc, spores borne in external flesh-coloured warts, 

 tetraspores cruciate immersed in the frond. ... Polyides. 

 Fronds attached by branching rhizoids, cystocarps, and tetraspores 

 immersed in the swollen tips of the branches, tetraspores zonate. 



Fastigiaria. 



69. Cystocarps immersed in the fronds. ... ... ... 70 



Cystocarps external, orate or urceolate, fronds traversed by a distinct 

 central filament or siphon. ... ... ... ... 71 



70. Fronds gelatinous, composed internally of a dense mass of slender 

 longitudinal filaments, which give off short, corymbose, lateral branches, 

 which form the cortex, spores in an irregular mass. Glceosiphonia. 

 Fronds soft, succulent, consisting -of an internal layer of slender 

 longitudinal filaments, and a cortex composed of roundish polygonal 

 cells, which become smaller towards the surface. Cystoclonium. 



71. Fronds rose-red, steins slender, ramuli simple,subulate, acute, apices not 

 involute, cystocarps stalked, alternating with the ramuli. Bonnemaisonia. 



Fronds dark-red, much branched, rather robust, superficial cells 

 small, polygonal, irregularly placed, apices of branches not involnte, 

 tetraspores in the young branches or palmately divided receptacles 

 (stichidia.) ... ... ... ... ... Rhodomela. 



Fronds purple or brownish-purple, superficial cells quadrate, apices of 

 the branches strongly involute, tetraspores in swollen pod-like 

 branches (stichidiaV ... ... ... ... Bostrychia. 



Fronds purple or red, occasionally blackish, either throughout or at 

 least in the youngbranches articulated, the articulations longitudinally 

 striate. ... ... ... ... ... ... 72 



72. Fronds brown-red (turning bright-red in fading) main stems corticated 



with irregular cells, densely clothed with bright red hairs, young 

 branches naked, tetraspores in swollen pod-like branches (stichidia). 



... Dasya. 

 Fronds purple or dark-red, tetraspores borne in the young branches. 



Polysiphonia. 



