RIIODOMELA. 



[ 658 ] 



RHOICOSPHENIA. 



Four i3iitisli species : R. styliformis, R. i 

 imhricata, li. setUjeray and R. (data. | 



R. (data (PI. 51. lig. 25). R. americana \ 

 (PI. 50. fifr. 46). 1 



The British species were obtained from I 

 t'^alpa, Ascidia, and NoctUiica. { 



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

 Kiitz. Sj). Ahj. 24; Bdghtwell, Micr. Jn. ! 

 1858, 94. 



RHODOM'ELA, Ag-.— A genus of Rho- 

 domelaceee (Eloiideous Algse), containing 

 two toleraljly common British species, with 

 feathery, inarticulate, branched fronds, the 

 branches composed of concentric layers of 

 oblong, colourless cells, with a cortical layer 

 of minute colom-ed cells. Colour of R. hjco- 

 podioides purplish brown, becoming black ; 

 height 4 to 18". Colour of R. snbfusca 

 brownish or reddish ; height 4 to 10". The 

 ceramidia are stalked on the ramuli, occur- 

 ring in summer ; the stivhidia, with tetra- 

 hedral tetraspores, occur in a similar situa- 

 tion in winter ; the antheridia (observed in 

 R. subfusca) also occur in tirfts in the same 

 position. 



BiBL. Harvey, 3Iar. Aly. 78; Tiilasne, 

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



miODOlMELA'CE^.— 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 (eeraviidia) 

 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. tetrasj>oret> 

 immersed in distorted ramuli or in lanceo- 

 late receptacles (sticJiidia), usually in rows. 



Synojysis of the British Oenera. 



Ochnthalia. Frond flattened, linear, ^\^th 

 an obsolete midrib, pinnatitid, alternately 

 inciso-dentate. 



Rhodomela. Irond 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. 



Rhytiphlcca. Frond cylindrical, inarti- 

 culate, transversely striate. Tetrasj:ores in 

 pod-like receptacles. 



Rolysi}>homa. Frond cylindrical, articu- 

 lated wholly or in part ; the branches longi- 

 tudinally streaked. Tetraspores in distorted 

 ramuli. 



Dasya. Frond cylindrical, the stem inar- 

 ticulate ; the ramuh articulated, composed 



of a single string of cells. 'Tetraspores in 

 pod-like receptacles (stichidia), borne by 

 the ramuli. 



RHOBOSPOR'E.E:. See Algje. 



RHODYME'NIA, Grev.— A genus of 

 Rhodj'meuificese (Florideous Algte), con- 

 taining seven British species, beautiful, 

 brightl3'--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. Rahnctta, PL 4. tig. 8'.) Most are not 

 more than 2" high, but R. laciniafa and 

 jjabncda gi'ow to 10" and 18". The coloiu' 

 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 di\-ided. The an- 

 theridia likewise form patches on the sur- 

 face of the frond, in R. Palutetta and palmata. 



BiBL. Harvey, Mar. Aly. 124, pi. 16 A; 

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



RHODYMENIA'CE.F:.— A family of 

 Floiideous Algas. Purplish or blood-red 

 sea-weeds, Avith an expanded or iiliform 

 inarticulate frond, composed of polygonal 

 cells ; occasionally traversed by a librous 

 axis. Superficial cells minute, irregularly 

 packed, or rarely arranged in filamentous 

 sei'ies. Fracti/icafion: 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- 

 mous or palmate. 



Stenoqramme. Conceptacles linear, rib- 

 like. 



Rhodyntenia. Conceptacles hemispherical, 

 scattered. 



** Frond compressed or terete, linear or 

 filiform, much branched. 



Sphcerococcus. Frond linear, compressed, 

 two-edged, distichously branched, with an 

 obscure midrib. 



Gracilaria. Frond filiform, compressed, 

 or flat, irregularly branched ; the central 

 cells very large. 



Ilypnea. Frond filiform, irregularly 

 branched, traversed bv a fibro-cellular axis. 



RIK )I(!(,)SPnE'NL\,Grunow.— A genus 

 of Biatomaeea?, = arcuate Gomphoneina w ith 



