which it bears only an outward resemblance, differing very essen- 
tially in microscopic characters. In the original P. spinulosa there 
are but four siphons surrounding the central cavity ; here there 
are twelve. By comparing the figure now given, with that of 
P. subulifera, t will be seen that there is a much nearer relation- 
ship to that species than to any other British one, and except 
for some differences of habit, and minor differences in structure, 
the two might perhaps be brought together. Prof. J. Agardh, 
however, who saw specimens of our P. simulans during his visit 
to England, pronounced them distinct, an opinion also enter- 
tamed by Mrs. Griffiths, and in which, though not without 
misgivings, I concur. As it is no longer possible to retain the 
name spinulosa for the plant here figured, I propose that of 
simulans, alluding to its deceptive character ;—for it looks some- 
times like P. subulifera, sometimes like P. nigrescens, and has 
been mistaken, as we have seen, for P. spinulosa. 
It is one of our rarer species, although found in several 
distant localities. 
Fig. 1. PotystpHONIA SIMULANS :—the natural size. 2. A small branch. 
3. Ceramidium. 4. Ramulus with imbedded tetraspores. 5. Joints from 
the stem, and young ramulus with apical fibres. 6. Transverse section of 
the stem :—all magnified. 
