150 IRIDJ2A. 



On rocks, &c. in deep pools, near low-water mark ; rather rare. Peren- 

 nial. Summer and Autumn. Found from Orkney to Cornwall, and on 

 the Irish coasts, but nowhere common. Stem minute, cylindrical, sud- 

 denly expanding into a roundish or reniform, undivided (or accidentally 

 cleft) frond, of a soft, thickish, membranaceous substance, becoming thin- 

 ner in drying, of a fine blood-red colour, and either simple, or bearing 

 along its margin lobes of a shape similar to the frond. The fronds vary 

 in diameter from 1 inch to 6, 8, and even 14 inches. Favellidia of small 

 size, thickly scattered over the surface of the frond ; tetraspores very mi- 

 nute, ternate, imbedded in the frond over which they are dispersed. 



2. K. Dubyi, Chauv. ; stem compressed, gradually ex- 

 panding into an obovate, simple, dull-red frond, wedge- 

 shaped at the base ; favellidia very minute, densely scattered 

 over the surface, jffarv. Phyc. Brit. t. cxxiii. 



On rocks, &c. within tide-marks, chiefly in land-locked bays. Annual. 

 Spring and early summer. Discovered at Falmouth by Miss Warren. 

 Plymouth Rev. W. S. Hore. West of Ireland. Fronds 6 12 inches 

 long, cuneateat base, obovate, at first quite simple, afterwards often torn. 

 Colour a dull, brownish red, becoming pale and yellow in old age. In form 

 this greatly resembles Iridcea edulis, while in structure and substance it 

 more nearly agrees with Kal. reniformis. 



XIV. TRID^A. Bory. [Plate 19, A.] 



Frond flat, carnoso-cartilaginous, dull red ; the central 

 substance composed of densely interwoven, longitudinal fi- 

 bres ; the periphery of closely-packed horizontal, moniliform 

 filaments. Fructification : 1, spherical masses of spores 

 (favellidia) immersed in the frond ; 2, tetraspores forming a 

 stratum at the base of the filaments of the periphery. Name 

 from Iris, the rainbow, because some species reflect prisma- 

 tic colours when growing under water. 



1. I. edulis, Stackh. ; frond simple, obovate or wedge- 

 shaped, rounded at the apex, gradually narrowing towards 

 the base into a short stem. Grev. Alg. Brit. p. 158, t. 17 ; 

 Hook. Br. Fl. ii. p. 308 ; Wyatt, Alg. Damn. No. 78 ; Harv. 

 Phyc. Brit. t. xcvii. Fucus edulis, E. Bot. t. 1307. 



On rocks and stones in the sea, common. Perennial. Autumn and 

 winter. Root an expanded disk, from which spring numerous, obovate, 

 obtuse, thick, cartilagineo-carnose or somewhat leathery fronds, 4 18 

 inches long, 2 8 inches wide, which gradually taper towards the base into 

 a short, linear stem ; undivided, but frequently cleft by the action of the 

 waves ; the margin smooth and even. The colour is a fine deep red, be- 

 coming much darker, frequently blackish when dried. Conceptacular 

 fructification near the extremity, in wide patches, frequently spreading over 

 a large portion of the frond, composed of globules of minute spores 

 imbedded in the substance. Tetraspores forming dense band-like sori, 



