154 RHODYMENIACE.E. v. 



poh'^fTonal cellules, smaller toward the surface. Conceptades immersed in the 

 branches beneath the peripheric stratum, but prominent to one side, the walls 

 formed of a dense plexus of filaments derived from the axis ; placenta fibro-cellular, 

 central, suspended in the cavity by slender filaments connected with the walls ; 

 spore-threads emitted in tufts from all sides of the centi-al placenta, moniliform, 

 fonnino- strings of spoix's in their articulations. Tetraspores dispersed through the 

 superficial stratum of the frond, oblong, zouate. 



I have already remarked under SoUeria the very close resemblance, in external 

 habit and in the structure of the frond, between the species of that genus and of 

 the present one. Indeed, except in the development of the spores, — a character, 

 however, which obliges us to refer them to widely distant Orders — the two genera 

 are undistinguishable. Ehahdonia was founded on two Australian Alg», very 

 similar in aspect to the plant now to be described ; and Prof. Agardh has added 

 four others, one of which is a native of the West Indies, and may possibly occur 

 at Key West. 



1. Rhabdonia Coulter i, Harv.; frond filiform, setaceous and bare of branches 

 below, gradually incrassated upwards, pinnate or sub-bi-pinnate above ; pinnae and 

 pinnulfe patent, lineari-fusiform, attenuate at the base, obtuse or sub-acute ; concep- 

 tades plentiful, half immersed, hemispherical ; tetraspores of large size, dispersed. 

 (Tab. XXIII. B.) Hypnea Coulteri, Harv. in Bot. Eapl. Exp. ined. 



Hab. Monterey, California, Dr. Conlter. North West Coast, Capt. Wilkes, (v. s. 

 in Herb. T.C.D.) 



Root a large disc, throwing oiF creeping fibres. Fronds densely tufted, 6 — 8 

 inches high, not thicker than hog's bristle below, gradually thickened upwards to 

 the diameter of a crow's quill. Stem once or sometimes twice forked within an 

 inch or two of the base, afterwards simple, naked for half its length, closely pin- 

 nate or occasionally bipinnate in its upper half; the pinns a line or two apart, very 

 patent, 2 — 3 inches long, the barren ones as thick as sparrow's quill, the fertile 

 ones twice or thrice that thickness. The pinnules when present are in all respects 

 similar, but are very irregularly placed, often secund. Conceptades large, plenti- 

 fully lodged in the lesser branches, prominent to one side, as if hemispherical or 

 sub-conical. Tetraspores dispersed in the branches. Colour a very dark, brownish 

 red. Substance cartilaginous. It shrinks and scarcely adheres to paper in drying. 

 Barren plants are setaceous, irregularly divided, and scarcely dilated upwards. 

 Tab. XXIII. B. Fig. 1. Rhabdonia Coulteri; the natural size. Fig. 2, longi- 

 tudinal section of a branch, showing tetraspores lodged in the surface cells ; fig. 3, 

 small portion of the periphery of the same, with two tetraspores ; fig. 4, transverse 

 section of a branch, cutting horizontally through a conceptacle ; fig. 5, portion of 



