CERAMIACE.E. 201 



nodes being transparent. — This contains C. echiono- 

 tum ; C. acanthonotum ; and C. ciliatum. 

 4. Frond covered throughout with small bark-cells, and 

 each node armed with a single spine. — This contains 

 C. Jlabelligerum. 



All the Ceramia possess very beautiful microscopic 

 characters ; and if these be carefully examined, most of 

 the species may be identified without difficulty. The 

 arrangement of the dark- coloured bark-cells round the 

 nodes gives to certain species the appearance of being 

 striped or variegated. The spines, or thorns, with which 

 the fronds of some kinds are armed are peculiar, — so far, 

 at least, as the British marine flora is concerned, — to 

 plants of this genus. They are very minute, and can 

 only be seen under the microscope ; but their effect is 

 very visible in the almost insurmountable difficulty that 

 is experienced when an attempt is made to disentangle 

 a bunch of fronds of a spinuliferous species. The 

 arrangement of the fronds in this genus is very sym- 

 metrical, and so is that of the branches, which are fan- 

 shaped, and seem to radiate from some common centre, 

 terminating in bifurcate, hooked tips. There is scarcely 

 any part of our coast where specimens cannot be obtained; 

 and the variations in which some of the species indulge 

 afford ample field for the exercise of all the observing fa- 

 culties, in the selection of complete series of the different 

 forms. It is, moreover, probable that there are even yet 

 new species to be discovered or determined, and that 

 patient observation may lead to the modification of the 

 existing arrangement of the British species. 



Ceramium rubrum. The red Ceramium. 



Frond from two to ten inches long, varying in thickness 



