Favelle \i-lobed, large, formed from truncated plumules. Colour a 
brownish-red, becoming orange in fresh water, and darker in drying. Swé- 
stance between cartilaginous and membranaceous, adhering, but not very 
closely, to paper in drying. 
PPP Enns nn 
Callithamnion tetragonum, when fully grown, is one of the 
largest and most robust and shrubby of the British species of 
this charming genus, and, seen under water, is an object of 
much beauty. In drying, though it sufficiently retains its form, 
it loses considerably in elegance, from the pressing together of 
the delicate quadrifarious ramuli, which in a state of nature stand 
out from the branchlets, giving to the different parts of the 
frond a roundness, without confusion, or matting together of the 
minutest part. These, in dried specimens, become confounded 
together. Its most frequent habitat is on the stems and margins 
of the lacinie of Laminaria digitata, which it frequently frmges 
in the most beautiful manner; but it is by no means confined 
to this species, beg often seen on some of the smaller Algz, 
as on Codium tomentosum, Chondrus crispus and others. It 
rapidly changes colour in fresh water, assuming a brilliant orange 
tint, and giving out a rose-coloured powder. Though a species 
of large size, its ¢etraspores are exceedingly small, much smaller 
in proportion than those of most other species, and, bemg borne 
near the tips of the smaller and more crowded ramuli may easily 
escape detection. The /avelle, on the contrary, are of large size, 
and easily seen. 
C. tetragonum appears to be of common occurrence on the 
shores of Europe, and very probably extends to the opposite side 
of the Atlantic. It is very closely, perhaps too closely, allied to 
C. brachiatum, Bonnem., which I have, therefore, figured on the 
following plate, that the distinctions may be more readily seen. 
Fig. 1. CALLITHAMNION TETRAGONUM :—the natural size. 2. Penultimate 
branch, set with plumules. 3. A plumule, bearing tetraspores. 4. Ra- 
~ mulus from the same. 5. A plumule bearing favelle. 6. Joints of one of 
the main branches, to show the veining :—al/ more or less magnified. 
