186 Mr. W. H. Harvey on a new British species o/Callithamnion. 



XXIV. — Description of a new British species of Callithamnion. 

 By W. H. Harvey, Esq., Trinity College, Dublin. 



[With a Plate.] 



In the year 1840 I received from the Rev. J. H. Pollexfen a Cal- 

 lithamnion gathered by him in the Orkney Islands so distinctly 

 characterized, that I had little difficulty in ascertaining it to be 

 new ; and, as a just tribute to its excellent discoverer, I named it 

 C. Pollexfenii. The MSS. of my f Manual of British Algae' had 

 at that time left my hands, but I forwarded a description of the 

 new Callithamnion for insertion in its proper place. By some 

 mischance the slip was mislaid and the book published without 

 any notice having been taken of it ; but under the MS. name of 

 C. Pollexfenii this beautiful plant has since been known to my 

 friends Mrs. Griffiths, Mr. ftalfs and others, and I only delayed 

 describing it till I should have an opportunity of revising the 

 whole of the British Callithamnia, a labour which has become 

 necessary from the many varieties of acknowledged species which 

 have come to my knowledge since the publication of the ' Manual/ 

 and some of which may perhaps be admitted eventually to the 

 rank of species. 



Having lately, however, received a specimen from Dr. Dickie of 

 Aberdeen, which exactly agrees with Mr. Pollexfen's, I no longer 

 delay giving a description of it, as follows : — 



Callithamnion Pollexfenii, Harv. Slender, flaccid, alternately much 

 branched ; branches linear, articulate, each joint having two oppo- 

 site, subulate, slender, short, spine-like, simple ramuli. 



On rocks in the sea. Orkney Islands, Rev. J. H. Pollexfen, 1840 ; 

 Aberdeen, Dr. Dickie, 1844, April. 



Filaments 1 — 2 inches high, tufted, very slender and flaccid, 

 repeatedly branched in an alternate manner, the major divisions 

 of the frond having a conical or spiry outline. Main stem undi- 

 vided, one-tubed, jointed and transparent, having several alter- 

 nate, erecto-patent, rather distant branches, which are again twice, 

 thrice or four times branched in a similar manner, each succeed- 

 ing series of branches being shorter than the preceding. Every 

 articulation, both of the stem, the branches and the lesser divi- 

 sions, emits, at a short distance below the joint or diaphragm, a 

 pair of erecto-patent, simple, subulate, short ramuli of much less 

 diameter than the joint from which they spring. Articulations 

 of the branches 4 — 8 times, of the ramuli once and a half, or twice 

 as long as broad. Colour a fine rosy red. Substance very tender. 

 Fruit unknown. It closely adheres to paper in drying. 



At first sight no species appears more isolated, and yet a slight 

 inspection will show that it is closely related to C. cruciatum, next 



