195 
sate appearance is due merely to the condition of mounted speci- 
mens distorted by pressure or other causes ? If so, the decussate 
appearance would be due to both surfaces of a normally spirally 
striated form being simultaneously seen, thus offering diamond- 
shaped reticulations, as Ralfs suggests (‘Brit. Desrn.,’ p. 220). 
When Dr. Barker first showed this form to Mr. Archer, they 
were both momentarily under the impression that the form 
presented a spiral fibre wound interiorly ; but a more accurate 
examination showed that the striae were really external. These, 
with the annular projections at intervals, gave the form a very 
marked appearance. Still, when viewed under a low power, there 
is just a possibility that this species might be mistaken for Penium 
margaritaceum , though no two species can be more distinct. — As 
regards the second (undulate) form shown by Dr. Barker, Mr. 
Archer ventured to think it must remain undecided whether this 
might be Pleurotcenium noibile (Richter) or Pleurotcenium dila- 
tatum (Cleve). Pending seeing actual specimens he would think it 
premature to decide. — The third form shown by Dr. Barker was 
equally certainly new to this country, but also equally hard to 
decide upon. It seems possibly the same as Docidium sceptrum 
(Kiitz.). 
In connexion with these forms Mr. Archer, whilst admitting the 
arrangement of the endochrome was seemingly a beautifully con- 
stant, and doubtless also an important character, would here desire 
to remark that Professor de Bary seemed to have somewhat mis- 
understood his (Mr. Archer’s) views on the subject, most likely 
from his not having clearly expressed them. All Mr. Archer would 
venture to propound was that he thought that matters were not 
as yet quite ripe for the adoption of the genus Pleurotsenium, and 
the last form drawn attention to by Dr. Barker seemed to bear 
out this view for the present. This was doubtless a species of 
Docidium (Breb.), but would just as doubtless be d priori placed 
in the genus Pleurotcenium (Nag.) by those who adopt that genus. 
But in the first specimens he had ever seen, when the gathering 
was fresher than now, there was just as little evidence as on the 
present occasion that the endochrome occurred in longitudinal 
parietal bands ; nay, it rather appeared to form an axile irregu- 
larly arranged mass. But on this point, touching this form, he 
would rather trust to its re-discovery and examination in a still 
fresher state. But further, as bearing on this genus (Pleurotse- 
nium, Nag.), that fine species, Staurastrum tumidum (Menegh., 
Breb., Ralfs, Kiitz. et auct.) is on all hands, even by those who 
adopt the genus Pleurotsenium, placed in Staurastrum ; yet it 
appears to be as truly a Pleurotsenium (in that its endochrome 
forms parietal bands, often, however, with numerous other granules 
obscuring this structure), as is de Bary’s Pleurotcenium turgidum 
( Cosmarium turgidum, Auct.), or even as the common Docidium 
Elirenbergii. This being the case, it is not impossible that certain 
other of the rarer forms, now referred from external figure to other 
genera, may be strictly referable to Pleurotsenium. Mr. Archer 
