RHIZOCLONIUM. 



[ 551 ] 



RHODOMELACE^E. 



Three British species (Smith) ; twelve 

 others (Kutzing). 



R. paradoxa (PI. 13. fig. 19). Stipes fili- 

 form, dichotomous ; frustules in front view 

 broadly wedge-shaped, somewhat acute at 

 the base. Length of frustules 1-540 to 

 1-480". 



RHIZOCLONIUM, Kiitz. A genus of 

 Confervaceae (Confervoid Algae), distin- 

 guished by the decumbent habit and the 

 short, root-like character of the branches. 



Kutzing includes here many of our British 

 Confervae : 



1. R. rimdare, C. Filaments simple, 

 diam. 1-900", fine bright green bundles 

 2 to 3 feet long ; in streams and rivers ; com- 

 mon (Dill. pi. 39). 



2. R. tortuosum, Dillw. Filaments sim- 

 ple, diam. 1-800", rigid, curled and twisted, 

 forming large strata; in salt-water pools; 

 abundant (Dillwyn, pi. 46). 



3. R. arenosum, Carm. Filaments simple, 

 diam. 1-1000 to 1-1800"; in dirty green 

 strata; sandy sea-shores. 



4. R. obtusangulum, Lyngb. (PI. 5. fig. 1 2). 

 Filaments branched, diam. 1-1400"; pale 

 green, stratified; sandy sea-shores. 



5. R. riparium (Jurgensii, Kiitz.). Fila- 

 ments branched, diam. 1-1400 to 1-1800". 

 Apparently not distinct from the preceding. 

 On sandy sea-shores ; not uncommon (Engl. 

 Botany, pi. 2100). 



6. R. implexum. Dillw. Filaments simple, 

 diam. 1-2000" ; bright green ; forming large 

 strata, on mountain rocks (Dillw. C. im- 

 plexa, tab. B). 



7. R. arenicolum, Berk. (Kochianum, Kz.). 

 Filament 1-2000 to 1-2400"; mountain 

 rocks (Berkeley, Gleanings, pi. 13. fig. 3). 



BIBL. Harvey, Brit. Mar. Alg. p. 206. 

 pi. 24 F; Kiitz. Sp. Alg. 385, Tab. Phyc. 

 Brit. Flora, ii. pt. 1. p. 354; Dillwyn, Brit. 

 Conferees. 



RHIZONOTIA, Ehr. A genus of Diato- 

 macese, of obscure structure. 



BIBL. Ehrenberg, Ber. d. Berl. Akad. 

 1843. 139. 



RHIZOPHORACEJ2. A family of Di- 

 cotyledonous plants, to which belong the 

 celebrated Mangrove-trees of the tropics. 

 They are remarkable for the general occur- 

 rence of a ramified form of liber-cell (PI. 39. 

 fig. 31). The long woody radicles pushed 

 out by the fruits, while still attached to the 

 parent tree, contain a vast quantity of these 

 ramified cells with very thick walls. 



RHIZOPODA, Duj. or better, Pseudo- 

 poda, E. A subdivision of the animal king- 



dom, comprising, according to Dujardin and 

 Ehrenberg, the Arcellina (with Dujardin's 

 genera Euglypha, Gromia, and Trinema) 

 and the Foraminifera. 



In Siebold's arrangement, it contains the 

 Amrebaea, the Arcellina, and the Foraminifera. 



The essential characters are the gelatinous 

 structureless composition of the body, and 

 the locomotive organs consisting of varia- 

 ble retractile root-like processes (false legs). 



BIBL. Dujardin, Infus. p. 240; Ehren- 

 berg, Infus.; Siebold, Vergl. Anat. 11. 



RHIZOSELENIA, Ehr. A doubtful ge- 

 nus of Diatomacese. 



Char. Lorica tubular, one end rounded 

 and closed, the other attenuate and multifid 

 or root-like. Marine (fossil). 



Six species (?). 



BIBL. Ehrenberg, Abh. d. Berl. Akad. 

 1841. 291 ; Kutzing, Sp. Alg. p. 24. 



RHODOMELA, Ag. A genus of Rhodo- 

 melaceae (Florideous Algae), containing two 

 tolerably common British species, with fea- 

 thery, inarticulate, branched fronds, the 

 branches composed of concentric layers of 

 oblong, colourless cells, with a cortical layer 

 of minute coloured cells. Colour of R. ly- 

 copodioides purplish-brown, becoming black; 

 height 4 to 18". Colour of R. subfusca 

 brownish or reddish ; height 4 to 10". The 

 ceramidia are stalked on the ramuli, occur- 

 ring in summer ; the sticMdia, 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, Brit. Mar. Alg. p. 78. 

 pi. 11. 13; Tulasne, Ann. des Sc. nat. 4 ser. 

 iii. p. 20. 



RHODOMELACE.E. 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 ramuli or in lanceolate 

 receptacles (stichidia), usually in rows. 



Synopsis of the British Genera. 



I. ODONTHALIA. Frond flattened, linear, 

 with an obsolete midrib, pinnatifid, alter- 

 nately inciso- dentate. 



II. RHODOMELA. Frond cylindrical, in- 

 articulate, opaque. Tetraspores contained 

 in pod-like receptacles (stichidia). 



