212 BRITISH SEA-WEEDS. 



lets, at first containing four sporules, subsequently eight or 

 more. 



In the c Phycologia Britannica ' this plant is called 

 P. sericea, and Dr. Harvey gives very elaborate reasons 

 for using that name, but in his more recent works he ap- 

 pears to acknowledge the prior claim of elegans, given 

 by M. Bonnemaison, and adopted by Kiitzing and 

 Agardh. I have, therefore, substituted elegans for sericea , 

 although the latter name is that best known to English 

 collectors. The fronds of this species are much narrower 

 than those of P. plumosa, and its mode of growth is very 

 different. It usually hangs in long tufts from the sides 

 of perpendicular or overhanging rocks, and is not con- 

 fined to any particular locality, but is generally distri- 

 buted all round our coasts. It is perennial, and in per- 

 fection during summer and autumn. 



Genus XCVII. DTTDKESETAIA. 



Frond cylindrical, very gelatinous, elastic, composed of 

 three series of threads ; the first or axial series loose netted, 

 anastomosing ; the second, closely packed, longitudinal, and 

 the third or outer series horizontal, forked, necklace-like. 

 Spores in globular masses, attached to the bark threads ; 

 tetraspores zonate, external, at the ends of the branches. — 

 Dudresnaia, in honour of M. Dudresnay. 



Under the new arrangement, which removed D. di- 

 varicata into a different Order, this genus contains only 

 one British species, confined to southern localities. 



Dudresnaia coccinea. The red Dudresnaia. 



Frond bright rosy-pink, from six to ten inches long, 

 tender, extremely gelatinous, much and irregularly branched; 



