ODONTHALIA. 77 



scorpioides is amphibious, growing, sometimes in the sea 

 and sometimes in ditches of brackish water, and a similar 

 indifference to habitat was observed by Dr. Hooker in 

 B. vaga, of Kerguelin's land. 



SYNOPSIS OF THE BRITISH GENERA. 



I. ODONTHALIA. Frond flattened, linear, with an obsolete 



midrib, pinnatifid, alternately inciso-dentate. [Plate 

 11, A.] 



II. RHODOMELA. Frond cylindrical, inarticulate, opake. 



Tetraspores contained in pod-like receptacles (sti- 

 chidia}. [Plate 11, B.J 



III. BOSTKYCHIA. Frond cylindrical, inarticulate, dotted ; 

 the surface cells quadrate. Tetraspores in terminal 

 pods. [Plate 11, C.] 



IV. RYTIPHLJSA. Frond cylindrical, inarticulate, trans- 

 versely striate. Tetraspores in pod-like receptacles. 

 [Plate 11, D.] 



V. POLYSIPHONIA. Frond cylindrical, articulated, wholly 



or in part ; the branches longitudinally striate. Te- 

 traspores in distorted ramuli. [Plate 12, A.] 



VI. DASYA. Frond cylindrical, the stem inarticulate ; the 

 ramuli articulated, composed of a single string of 

 cells. Tetraspores in pod-like receptacles (stichidia], 

 borne by the ramuli. [Plate 12, B.] 



I. ODONTHALIA. Lyngb. [Plate 11, A.] 



Frond plano-convex, two-edged, vinous-red, distichous, 

 obsoletely ribbed, alternately toothed at the margin, cellular; 

 central and surface-cellules minute, irregular. Fructification 

 twofold, on distinct plants ; 1, ceramidia, containing a tuft 

 of pear-shaped spores ; 2, lanceolate pods (stichidia] con- 

 taining tetraspores in a double row. Name, otiovg, a tooth, 

 and 0Xo{, a branch. 



