m 



STXOrsiN OF BRITISH -KAWEEDS. 



J[i(h. Very pare. Thrown up, probably from deep water. An- 

 nual. June to August. 

 To Mrs. Griffiths this species lias been familiar for 

 thirty years under the colloquial name " Orangt Thoa/rf" 

 which at once expresses its usually small Bize, as compared 

 with others of the genus, and the rapid change of colour 

 which it undergoes on touching fresh water. The last 

 peculiarity is so striking that a passing shower of rain has 

 often betrayed it to Mrs. Griffiths, when before the shower 

 it had passed unnoticed among other red plants. Dr. 

 Greville, in his ' Cryptogamic Flora,' considers it identical 

 with N. Bonnemaisoni, an opinion which he subsequently 

 abandoned ; and in his ' Algae Britannicse' he refers it to 

 JV. Gmclini. I consider it to be distinct from both these 

 species, at the same time admitting that it borders very 

 closely on both, and that in the absence of a knowledge 

 of its fructification it is difficult to fix on a very tangible 

 distinguishing character. 



LIU. PLOCAMIUM. 



1/4. coccineum {The scarlet Plocamitcm) ; frond narrow, car- 

 tilaginous, piano-compressed ; branches irregularly alternate, 

 patent ; ramuli subulate, second, three or four consecutively, 

 pectinate on their inner edges ; tubercles lateral, sessile : 

 stichidia scattered, lanceolate, simple or branched, Lynyh. 

 Byd. Ban. p. 39. t. 9. (Atlas, PL XXXIX. Fig. 178.) 

 Plocamium vulgare, Lamour. P. Lyngbyanum, Ktz. P. Bin- 

 derianum, Ktz. Delesseria coccinea, Ay. D. Plocamium, 

 Ay. Ceramium Plocamium, Both. Fucus coccineus, Buds. 

 F. Plocamium, Gm. Plocamium fenestratum, Ktz. 

 Bab. On submarine rocks and larger Alga?, generally beyond 

 tide-level. Perennial. Summer and autumn. Common. 

 A well-known, abundant, and beautiful species, and an 

 especial favourite with amateur weed-collectors, and manu- 

 facturers of seaweed pictures. With the exception of 

 this pelagic species, the genus Plocamium, in which I 

 include the Thamnophora of Agardh, and the Thamno- 

 carpus of Kiitzing (not of Harv. in Hook. Ic. Plant.), is 

 confined to the Southern Ocean, where many very distinct 

 species are found, some of which are of large size, having 

 brilliant crimson or rose-red fronds from a quarter to half 

 an inch in breadth, and elegantly pectinato-pinnate. To 

 all, the alternate, or secund, acute ramuli are common ; 

 the only variation being, that in some they are deltoid, in 



