87 
On Ruasponema, and a New ALuiep GrENvs. 
By G. A. Warxer-Arnort, LL.D. 
Tue late Professor Smith was justly entitled to be placed 
at the head of those whose attention was directed to the 
Diatomacez. Possessed of excellent instruments, and of a 
mind clear and discriminating as to what the limits of a 
genus or species were, he was alone qualified, if he had ob- 
tained access to authentic perfect specimens, to correct the 
unavoidable errors of Kutzing, or extract what is valuable 
from the chaotic writings of Ehrenberg; the latter of whom, 
by his figures of numerous forms of which he had only seen 
very imperfect specimens, unaccompanied by precise, suffi- 
cient diagnostical characters, has done more to cumber the 
science with a load of useless names than can be rectified 
for many years to come. 
So long as Smith survived, I preferred committing my 
notes to him to dispose of as he thought proper, his senti- 
ments being in accordance with my own,—that it is better 
not to publish a new species, or give it a name, than to do 
so from scanty or imperfect materials which leave both genus 
and species doubtful. Even now I have some hesitation in 
writing on the subject, as my views are diametrically opposed 
to those who consider it necessary to give names to forms 
which, to the eye, appear distinct, but which have not struc- 
tural differences sufficient for a specific character; and this 
alone entitles them to be acknowledged or referred to by 
others. 
In the following I shall endeavour to make the characters 
as clear as possible. 
Smith has first correctly defined and explained the struc- 
ture of Rhabdonema. Each frustule of this genus has two 
valves or ends, which are alike, and marked with moniliform 
strie; these valves are separated by several annuli, which 
are cellulate; the annuli project into the interior septa, 
which are open in the middle. These septa are sometimes 
projected from the whole imner surface of the annulus; 
sometimes from one half only, and consequently do not then 
pass beyond the central aperture: the first are called oppo- 
site, the last alternate, septa; in either case, each septum is 
supposed to terminate at the middle; they may be entire, or 
with openings when they are said to be perforate. 
As many merely consult figures, it is necessary that I 
request my readers to keep the above in recollection ; or, if they 
possess Smith’s second volume of the ‘ Synopsis of British 
