494 DESCEiPTioN OF [Polffffastrica 



MicROMEGA hyalopus. — Colourless at the base, hyaline, branches green, 

 narrow, numerous, tapering to the apex, tufted ; the lower rows of 

 navicul® loose, the upper more closely approximate ; internal tubules 

 obsolete ; naviculae on secondary side lanceolate ; on the other aspect' 

 oblong, truncate. Length of frond half inch- 



M. ramosissimum. — Setaceous above the base, rigid, di or tri-choto- 

 mous, superior branches very numerous, capillary, in a closely set 

 whorl, more or less elongated ; naviculae in close rows, their tubes 

 distinct; their length l-720th ; lanceolate on one side, oblong, linear, 

 and truncate on the other. Length of frond 1 to 2 inches. 



M. setaceum. — Setaceous, olive-coloured, rigid, sub-dichotomous, 

 lateral and terminal branches short and spiny j naviculae in close 

 rows, lanceolate, acute on one side ; on the other truncate. Length of 

 naviculee l-696th to l-720th. Length of fi-ond l-12th to 1 inch. 



M. aureum. — Arborescent, setaceous above the base, rather rigid 

 ochre-coloured, much branched, branches dense, capillary, pale, 

 slender, and mucous ; rows of naviculae close ; tubules distinct ; 

 naviculae on one side lanceolate, on the other oblong and truncate ; 

 their length 1 -960th. Length of frond 1 to IJ inch. 



M. corxjmbosum. — Arborescent, rather stout at the base, firm, rigid, 

 of a yellowish olive colour ; much branched, the branches setaceous, 

 rigid, and disposed in a corymbose manner ; the series of naviculae 

 and tubules distinct, close ; the naviculae elKptic-lanceolate ; on one 

 side oblong and truncate. Length 1 -960th. Length of frond \\ inch. 



M. myxacanthurn. — Less stout, gelatinous, cartilaginous, pale 

 brown, branches divergent, attenuate at the base, multifid and digi- 

 tate at the apex, the gaping incisions acute ; naviculae lanceolate, in 

 fewer and looser rows below, in closer ones above. Length of navi- 

 culae l-790th to l-650th. 



M. apiculatum. — Setaceous, olive-coloured, rigid, branches erect, 

 dilated, and acute at the apex, lancinated throughout; series of 

 naviculae close ; secondary tubules distinct ; naviculae lanceolate, the 

 other side oblong, truncate. Length 1 -650th. Length of frond 

 half-inch. 



M. Medusinum. — Cartilaginous, gelatinous, hyaline, and brownish, 

 tui'gid at the base, branches irregular, much thickened at the base, 



