swollen dissepiments :—those of the ramuli uniformly about twice as long 
as broad. Favelle solitary or binate, bursting from the rachis of the plu- 
mules, variously lobed. Tetraspores minute, globose, terminal on the 
ultimate ramuli. Colour a rosy pink, or brownish red. Substance deli- 
cately membranaceous, soft and flaccid, most closely adhering to paper. 
One of the most concinnate of the Callithamnia, elegant in all 
its minute parts, and strictly neat in its mode of growth. In 
essential character it closely approaches C. gracillimum, from which 
it is more to be distinguished by habit than by any very definite 
character. C. gracillimum is a larger and more tufted plant, 
more regular in ramification, with longer and more indefinite 
plumules, varying much in the composition of its ramuli. Our 
present plant is rather robust, with an evident central stem and 
lateral branches, spreading with much regularity ; each branch, 
as well as the plumules with which it is feathered, being of a 
narrow lanceolate outline. The plumules are very generally 
triply pinnate. Favelle are much less commonly found on this 
species than tetraspores, and generally burst from the sides, and 
not the apex of a branchlet. 
Though found in many places, C. thuyoideum roust be ranked 
among the rarer forms of the genus. 
Fig. 1. CALLITHAMNION THUYOIDEUM ; a frond :—of the natural size. 2. Two 
articulations from a branch, each bearing a plumule. 3. Pinna from the 
same, with tetraspores. 4. A tetraspore. 5. Abbreviated plumule bearing 
a favella :—all more or less highly magnified. 
