116 BRITISH MARINE ALG. 
by the late Sir John Richardson, is unknown to me. P. Griffithsianes 
now regarded as a variety of P. subulata, is found growing on Polyida, 
lumbricalis (Fig. 83), in Torbay, though rarely. P. Grevillii found by Dr. 
Greville on the shores of Bute, parasitical on the larger shore weeds. P. 
Carmicheliana, now a variety of P. fibrillosa, found growing on Desmarestia 
aculeata (Fig. 52) by Captain Carmichael. P. obscura, a small and rather 
insignificant species, growing in out-of-the-way places, on the roots of the 
Fuci and on submerged rocks. P. simulans, a rare though widely- 
dispersed species. It has somewhat the appearance of P. spinulosa, the 
stems being like those of that species, set with spines or short pointed 
ramuli, which hold the branches of the plant together, trying the patience 
of the manipulator in disentangling them. Its similarity to some other 
species is referred to in the specific name of Simulans. P. subulifera is 
another spine-bearing species, possessing little beauty, and not frequently 
met with, though dispersed along the coasts of England and Ireland. P. 
furcellata is a rare and very pretty little species, all the branches being 
terminated by a little fork, the tips of which incline upwards. This 
interesting plant is a deep water species. I dredged it in Plymouth Sound 
some years ago, but have never found it since. It was taken formerly at 
Sidmouth and dredged in Torbay, but for many years it has disappeared 
from every locality in which I have sought it. This rareness of some 
species and occasional disappearance, at least for several seasons, in others, 
is certainly very curious, and has often formed the subject of ingenious 
speculation. The causes are doubtless natural enough, if known ; but here 
I can do no more than record the fact, that while some species are 
abundant, and make their appearance in the same situations with tolerable 
regularity, others are rare, and occasionally disappear for many seasons 
together, then suddenly reappear in their former habitats, and again as 
unaccountably disappear. The genus Polysiphonia contains one species 
which was discovered subsequently to the publication of the “ Phycologia 
Britannica.’”’ Its name is Polysiphonia fetidissima, so called on account 
of the strong and by no means agreeable odour which it emits during the 
process of mounting, forming a strange contrast to that of other species, 
some of which exhale a perfume as delicate as violets. P. foetidissima is 
very similar in growth and ramification to P. fibrata, and indeed some algo- 
logists, I believe, consider it to be merely a variety of P. fibrata, though 
the colour is very much darker, inclining to a blackish tint; and it is 
curious that the odour emitted by each of these species is alike, that of 
_ P. fetidissima being rather the more disagreeable of the two. 
The genus Dasya, or hairy-branch, is a numerous and considerably 
diversified group of plants, all being more or less remarkable for their 
brilliant crimson hue. Of the British species, the largest and most 
abundant is the handsome and well-known Dasya coccinea, or the scarlet 
dasya, a branch of which is represented slightly magnified at Fig. 108. 
The plants in this group are chiefly characterised by the tufts of thread- 
like jointed ramuli which clothe all the branches of these algw, and are of 
