NARRATIVE OF THE CRUISE. 
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pelagic and littoral floras, in the former I have never detected frustules of Achnanthes , 
Rhabdonema, Grammatophora, or of Cocconeis and other genera which resemble these 
in being stipitate, adnate, or attached to each other in some other manner. 
“ Another observation, made during the examination of these surface gatherings, is 
that when the net yielded an abundance of different forms of microscopic animals, 
Diatoms were extremely rare ; for this I have been unable to suggest any explanation 
other than that the Diatoms serve as food to the animals, so that where the latter are 
abundant the former are few in number. 
“The dredgings in the Antarctic Ocean, and especially that south of Heard 
Island, were very anomalous, showing frustules of freshwater Diatoms, such as Asterionella 
formosa and Ceratoneis arcus, along with forms which are entirely marine. This 
anomaly is, I believe, to be explained by regarding these terrestrial Diatoms, and 
especially Ceratoneis (which grows' only at upwards of 300 feet above sea level), as the 
remnants of icebergs, which slowly melted and deposited their delicate load of Diatoms 
which grew upon them whilst they formed part of the virgin ice. 
“ Although I have been obliged to make large additions to the number of genera and 
species, my observations of the surface gatherings have, at the same time, led me 
to recognise the variability of certain genera such as Goniothecium, Dicladia, and 
by analogy Syndendrium. This is also the case with the sporangia! forms of different 
species of Chcetoceros, and also Euodia and Coscinodiscus, in which I have observed 
two different valves of the same frustule, one being provided with a ‘ pseudo- 
nodulated ’ margin, the other without. In the same way I have noticed marked 
differences in the two valves of the same Coscinodiscus, which, if they had been found 
apart, would certainly have been referred to two different species. 
. “In these collections I have had the pleasure of recognising certain new types, 
which I discovered some years ago in the Adriatic, but of which I have hitherto 
deferred the publication. One of these is Rhizosolenia (?) jlaccida, which, however, I 
hesitate to refer to that genus, not having been able to observe the terminal calyptra ; 
the other is the type upon which Grunow founded the genus Thalassiothrix, a name 
which I retain out of respect to the author, although I must somewhat alter the account 
of it, having observed it several times alive and in different conditions. 
“ In conclusion we are indebted to the Naturalists on board the Challenger for the 
knowledge of several new discoidal forms remarkable for their size (sometimes as much 
as several millimetres in diameter), for the extreme tenuity of their walls and the 
delicacy of their sculpturing. The size of the frustules and the tenuity of the walls 
interfere with the possibility of recognizing such organisms even though they be of 
frequent occurrence ; and in fact in many of the soundings entrusted to me, as well as 
in many marine deposits from America, I have recognised large fragments of finely 
granulated silica, which I now believe to have belonged to large discoidal Diatoms, 
