(172) 



the upper part these veins are wanting, and the articulations are distinct, 

 and gradually become shorter upwards. Substance rather soft and 

 flaccid, and adhering, but not very firmly, to the paper. Colour, a 

 rather bright purplish lake, but often changing to a reddish or even 

 yellowish brown, without gloss. Favellae clustered at or near the apices 

 of abbreviated branchlets, spores large, angular. Tetraspores numerous, 

 arranged along the upper edge of the pinnules, roundish oval, sessile and 

 triparted. 



C. roseum is one of our most common species, being very generally 

 distributed all round the British shores, and is equally abundant on the 

 east and on the west coasts, growing sometimes in great abundance on 

 rocks that are bare at low water, or occasionally at gi-eater depths 

 generally, however, attached to the smaller Algae, such as Ceramium, Cla- 

 dostephus, &c., generally growing in separate tufts, but these often cover 

 a considerable extent of surface. We have sometimes seen it forming 

 a dense covering on the roofs of small submarine hollows or caves, the 

 fronds brushed down in fine crossing tessellated ridges, so as to resemble 

 the woodwork on the roofs of cathedrals, &c. 



Its principal characters are found in its long joints, opaque stems, and 

 slender pinnae, by which it is not generally difficult to distinguish it 

 from its allies. In specimens that have never been exposed to the 

 atmosphere, the colom* is generally a fine clear lake, but the action of 

 the air soon changes the colour to a more or less yellowish brown, and 

 specimens may be often seen with the exposed parts brown, and the 

 under parts still retaining their original purple coloiu-. 



EXPLANATION OF PLATE CXXV. 



Fig. 1. — Callithamnion roseum, natural size. 

 2. — Pinnule with tetraspores. 

 8. — Teti'aspore from same. 

 4. — Pinnaj with favella^. 

 5. — Portion of stem. All magnified. 



