BARKAS, ON BACILLARIA CURSORIA. 253 
occasional frustule of Nav. pseudo-lbellus. On June 5th 
another gathering from the same locality contained almost 
exclusively B. cursoria so abundantly that, when viewed upon 
a slide, the field of the microscope presented the appearance 
of a racecourse with rows of frustules pushing and running in 
all directions. Specimens of this beautiful diatom I for- 
warded, living, to Mr. Norman, of Hull; Mr. Baker, of 
Liverpool ; and Dr. Donkin, of Newcastle, the latter gentle- 
man being the discoverer and describer of the variety. (See 
‘Quart. Jour. Mic. Sci.,’ Vol. VI, New Series, p. 16.) 
There are a few features in relation to B. cursoria worthy 
of notice. First, that in all specimens I have gathered they 
are entirely covered with a kind of gritty matter, as though 
they were enveloped in some adhesive mucus which caused 
small particles to adhere to them. This condition is peculiar 
to B. cursoria, as the other Diatomacez in the same gather- 
ings are clean, and free from attachments of any kind. The 
second is, that the force with which they move appears quite 
disproportionate to their size and apparent strength. Dr. 
Donkin, in his excellent description of them in the article 
before referred to, says he has observed them push away 
“« A. arenaria, a species at least six times their own size.” [ 
have frequently seen them push away particles of foreign 
matter, and that with the greatest apparent ease, at least one 
hundred times larger than all the frustules combined; and 
what is more remarkable still is, that they not only push 
the accumulated particles away when they are in their direct 
line of motion, but, if they merely touch them in passing, 
they drag them after them as though they were literally held 
by some magnetic attraction or strong cement. Third, Dr. 
Donkin very graphically describes one phase of the curious 
motions of B. cursoria,* viz. that in which the frustule on 
one side of a cluster appears fixed, and the other frustules 
move past each other in rapid succession. I have seen that 
motion frequently; but I have also frequently seen the 
frustule which at one time was fixed become loose, and the 
frustule at the opposite side of the cluster fix itself, 
and the remainder move with great freedom. I have also 
observed the same cluster free at both sides, and each side 
move at the same time in opposite directions, somewhat 
similar to the motion of B. paradowxa, as described in Smith’s 
‘Synopsis.’ I have also observed the centre frustule become 
stationary, and those at each side rush backwards and for- 
wards with great speed. I have seen frustules, to the number 
of fifty, grouped together, move rapidly until they formed a 
* ‘Quart. Journ. Mic. Sci.,’ Vol. VI, p. 17. 
