This species was first collected, it would seem, by Dr. Jacob 
at Whitsand bay, and first recognised as new by Professor 
Walker Arnott, from whom I first received specimens under this 
name,—a name adopted in the British Flora, and now generally 
recognised. /. byssoideum is one of the softest and most gelati- 
nous of the genus, having exceedingly slender fronds, growing in 
dense tufts. To the naked eye it frequently bears much resem- 
blance to C. corymbosum, so much that it sometimes requires a 
microscope to determine to which species the specimen under 
examination may belong. The ultimate branching, and the posi- 
tion of the tetraspores will then afford an easily seen character, 
by which the two plants may be distinguished. There is a much 
closer affinity, indeed, between C. byssoidewm and C. roseum, 
than between the former and C. corymbosum. From C. roseum 
our plant is chiefly known by its much greater delicacy and 
softer substance, and its adhering much more closely to paper, 
and being more glossy when dry. 
Fig. 1. CALLITHAMNION BYSSOIDEUM; a tuft :—of the natural size. 2. Part of 
branch, with bipinnate plumule. 3. Pinnules, bearing tetraspores from 
the same. 4. Part of a branch with favelle. 5. A favella. 6. Articula- 
tions from the lower part of the stem :—all more or less highly magnified.- 
es 
