Ceramium acanthonotum was first distinguished by the late 
Capt. Carmichael, of Appin, in whose unpublished ‘ Algze Appin- 
enses’ an excellent description and accurate figure are given. 
It is my fault that in the ‘ British Flora’, and subsequent works, 
it appears only in the rank of a variety. Later observations, on 
several of our shores, and comparison of numerous specimens, 
from various quarters, have long since convinced me that it is a 
true species. Its colour is much darker than that of C. ciliatum, 
often an intense purple; and the tufts are usually shorter, and 
more densely compacted. ‘These characters, however, are not 
sufficiently definite, and an appeal to the microscope may be 
necessary. ‘This at once displays the admirable character by which 
the species may be recognized, namely, the solitary, three-joited 
spine, arming the outer margin of every jomt. The only other 
known British Ceramium which has a spine at all similar, is 
C. flabelligerum, but that is at once distinguished by its joints 
being coloured, not hyaline; not to speak of its very different: 
branching, and the smallness of its spine. 
Kiitzing, im his revision of the genus Ceramium, divides the 
species into six distinct genera, one of which he founds on 
the present individual, which he distinguishes generically from 
other ciliated Ceramia because its tetraspores are erumpent. As 
some of my readers may desire to know the characters attributed 
to this author’s genera, they are here given. 
Hormoceras. Frond jointed; cortical cells collected at the dissepiments in trans- 
verse zones; tetraspores immersed. (C. diaphanum and its allies ; 
thirteen species enumerated.) 
Goneroceras. Frond jointed; cortical cells collected at the dissepiments in 
transverse zones ; tetraspores erumpent. (C. Deslongchampsii, and 
Jive others.) p 
Ecurnoceras. Frond jointed, zoned and aculeated at the joints; tetraspores 
immersed. (C. ciliatum, and nine others.) 
Acantuoceras. Frond jointed, zoned and aculeated at the joints; tetraspores 
erumpent. (C. acanthonotum.) 
Creramium. Frond filiform, consisting of a jointed central axis, and a cortical, 
continuous layer of cells, destitute of cilia or spines; tetraspores 
immersed in the cortical layer. (C. rubrum., §c.) 
Crenrroceras. Frond as in Ceramium, but furnished at the joits with prickles 
or spikes; tetraspores erumpent. (C. clavulatum, and five others.) 
Fig. 1. Ceramrum AcanTHoNoTUM :—tuft of the natural size. 2. Portion of a 
filament. 3. Small part of the same, with ¢e¢raspores. 3. Small portion 
of a filament, with a favella, in situ :—all more or less magnified. 
