RHODOMELA. 



[ 658 ] 



RHOICOSPHENIA. 



Four British species : R. styliformis, JR. 

 imbricata, R. setigera, and R. alata. 



R. alata (PI. 51. fig. 25). R. americana 

 (PI. r,o. fig. 46). 



The British species were obtained from 

 Sal pa, Ascidia, and Noctiluca. 



BIBL. Ehr. Abh. Berl Ak. 1841, 291 ; 

 Kiitz. Sp. Ala. 24; Brightwell, Micr. Jn. 

 1858, 94. 



RHODOM'ELA, Ag. A genus of Rho- 

 domelaceae (Florideous Algae), containing 

 two tolerably common British species, with 

 feathery, inarticulate, branched fronds, the 

 branches composed of concentric layers of 

 oblong, colourless cells, with a cortical layer 

 of minute coloured cells. Colour of R. lyco- 

 podioides purplish brown, becoming black ; ! 

 height 4 to 18". Colour of R. subfasca \ 

 brownish or reddish ; height 4 to 10". The 

 ceramidia are stalked on the rainuli, occur- 

 ring in summer ; the stichidia, with tetra- 

 hedral tetraspores, occur in a similar situa- 

 tion in winter ; the antheridia (observed in 

 R. subfusca) also occur in tufts in the same 

 position. 



BIBL. Harvey, Mar. Alg. 78; Tulasne, 

 Ann. Sc. Nat. 4. iii. 20. 



RHODOMELA'CEvE. A family of Flo- 

 rideous Algae. Red or brown sea-weeds, 

 with a leafy or filiform, areolated or articu- 

 lated frond, composed of polygonal cells. 

 Fructification: 1. Conceptacles (ceramidia) 

 external, ovate or urn-shaped, furnished 

 with a terminal pore, and containing a tuft 

 of pear-shaped spores ; 2. antheridia, borne 

 in tufts in similar situations ; 3. tetraspores 

 immersed in distorted raniuli or in lanceo- 

 late receptacles (stichidia), usually in rows. 



Synopsis of the British Genera. 



Odonthalia. Frolid flattened, linear, with 

 an obsolete midrib, piunatifid, alternately 

 inciso-dentate. 



Rhodomela. frond cylindrical, inarti- 

 culate, opaque. Tetraspores contained in 

 pod-like receptacles (stichidia). 



Bostrychia. Frond cylindrical, inarticu- 

 late, dotted; the surface-cells quadrate. 

 Tetraspores in terminal pods. 



Rhytiphlcea. Frond cylindrical, inarti- 

 culate, transversely striate. Tetrasjcores in 

 pod-like receptacles. 



Polysiphoma. Frond cylindrical, articu- 

 lated wholly or in part ; the branches longi- 

 tudinally streaked. Tetraspores in distorted 

 ramuli. 



Dasya. Frond cvlindrical, the stem inar- 

 ticulate ; the ramuli articulated, composed 



of a single string of cells. Tetraspores in 

 pod-like receptacles (stichidia'), borne by 

 the ramuli. 



RHODOSPOR'E^. See ALGJE. 



RHODYME'NIA, Grev. A genus of 

 Rhodymeniaceae (Florideous Atoae), con- 

 taining seven British species, beautiful, 

 brightly-coloured sea-weeds, growing on 

 rocks or larger Algae, having a flat mem- 

 branous or somewhat leathery frond, ribless 

 and veinless, of parenchymatous texture. 

 (R. Palmetta, PL 4. fig. 8.) Most are not 

 more than 2" high, but R. laciniata and 

 palmata grow to 10" and 18". The colour 

 is mostly rose- or blood-red. The coccidia 

 are formed on the lacerated margins or the 

 tips of lobes of the frond. The tetraspores 

 form cloudy spots along the margin, or are 

 scattered, tetrahedrally divided. The an- 

 theridia likewise form patches on the sur- 

 face of the frond, in R. Palmetta a,n& palmata. 



BIBL. Harvey, Mar. Ala. 124, pi. 16 A ; 

 Thuret, Ann. Sc. Nat. 4. iii. p. 19, pi. 3. 



RHODYMENIA'CE^E. A family of 

 Florideous Algae. Purplish or blood-red 

 sea-weeds, with an expanded or filiform 

 inarticulate frond, composed of polygonal 

 cells; occasionally traversed by a fibrous 

 axis. Superficial cells minute, irregularly 

 packed, or rarely arranged in filamentous 

 series. Fructification : 1 . Conceptacles (coc- 

 cidia), external or half-immersed, globose or 

 hemispherical, imperforate, containing be- 

 neath a thick envelope a mass of spores 

 affixed to a central column ; 2. antheridia, 

 collected in flat patches or sori ; 3. tetra- 

 spores, either dispersed through the whole 

 frond, or collected in indefinite cloudy 

 patches. British Genera : 



* Frond flat, expanded, leaf -like, dichoto- 

 nious or palmate. 



Stenogramme. Conceptacles linear, rib- 

 like. 



Rhodymenia. Conceptacles hemispherical, 

 scattered. 



** Frond compressed or terete, linear or 

 filiform, much branched. 



tipharococcus. Frond linear, compressed, 

 two-edged, distichously branched, with an 

 obscure midrib. 



Oracilaria. Frond filiform, compressed, 

 or flat, irregularly branched ; the central 

 cells very large. 



Hypnea. Frond filiform, irregularly 

 branched, traversed by a fibro-cellular axis. 



RII01COSPHE'NiA,Grunow. A genus 

 of Diatoniaceae, = arcuate Gomphonema with 



