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152 NOTES ON RANGE IN DEPTH OP MARINE ALGM.
lead from the Abrolhos shoal, in 40 fathoms, in lat. 18° 11" S., long.
32° 43' 15" W., thirty miles frpm the nearest part of the coast of
Brazil. Most of it consisted of a species of Melobesia, much decayed,
but partly also fresh and entire ; adhering to it, growing on it, in fact,
there is a solitary specimen of an Alga of bright crimson. On exami-
nation I had no hesitation in referring it to the genus Peyssonelia. It
is not very prudent to describe supposed new species from solitary
examples ; nevertheless, as it seems to differ from others known to me,
and being of interest in relation to the subject, it may be legitimate to
record it under the provisional name Peyssonelia ubyssicola, sp. n.* If
a single cast of the sounding-lead did such good service, how much
more would the dredge accomplish on this Abrolhos shoal ?
Finally, it is worthy of notice, that species which reach the lowest
depth where Algce vegetate are chiefly Rhodosperms ; next in order
the olive-coloured. The Chlorosperms prevail in the littoral and
upper part of the laminarian zones.
BiatomacerB are usually considered to rank among the lower forms
of AUjrB. I may close with a brief reference to their range. Although
some few species have been certainly brought up from the greatest
depths reached by the dredge, it does not necessarily follow that they
live and propagate there. Many of the marine species adhere to the
higher forms of seaweeds, and necessarily have a limited range ; while
not a few of the free species occur at or not far below the surface.
Along with the Delesseria already mentioned as growing at 80 fathoms,
1 only detected three Diatoms, viz. Mdosira marina, Coscinodiscus
radiatus, and C. eccentricus. These minute organisms are so inde-
structible, so abundant, and widely diffused, that it is not surprising
to find tlunn in matter dredged at various depths. The Melobesia
from the Abrolhos shoal yielded at least a dozen species, but I cannot
positively assert that they were living.
It is to be hoped that in future more attention will be paid to this
subject. Exact records of depth will add to the interest pertaining to
the Algre procured, besides contributing to a department of inquiry very
much overlooked ; in this respect zoologists are far ahead of algolo-
gists..
* Peyssonelia abyssicola. Nearly circular, faintly zoned concentrically, subtomcntose
beneath, about, half an inch in diameter ; colour bright red ; upon
Lithothamnitim mamillare (Melobesia mamillaris, Harvey).