Norers zx Reprty to Dr. WaLKEeR-ARNOTT. 
By Dr. Donxin. 
Proressor Walker-Arnott having considered it proper to 
attack me in the preceding number of this Journal (p. 164), 
on certain facts demonstrated by me in my paper on the 
‘Marine Diatomacee of Northumberland, * I consider it 
my duty to offer a reply. 
I confess myself at a loss to comprehend Dr. Arnott’s 
reason for accusing me of having acted towards him with 
want of courtesy. But J presume it is because I have pointed 
out, in the postscript of my paper, that my P/. rectum, n. sp., 
is identical with that form to which he has given the cogno- 
men of Apr. Ralfsii. Dr. Arnott imagines I had no right to 
mention his name in the matter, because he had not then 
published his description of the form in question. But he 
evidently forgets that at the period when the postscript of 
my paper was written, slides had been distributed amongst 
observers (mounted from Mr. Ralfs’ Penzance gathering) 
containing this species in abundance, with his—Dr. Arnott’s 
—generic and specific name appended. + Thus, then, it is 
evident that the name given by Dr. Arnott to a particular 
diatomaceous form became, actually and virtually, published. 
I therefore, after examining well authenticated specimens of 
this same form, had a perfect right to criticise, in any becom- 
ing manner, Dr. Arnott’s conclusion and synonyme; and 
more especially so when I knew that I had previously de- 
scribed to the Microscopical Society{ the very same species 
under a different name. 
Now it appears to me that Dr. Arnott would have acted 
much more in that spirit which ought to guide every philo- 
sophical discussion, had he, instead of accusing me of being 
guilty of a grave social offence, attempted to refute the accu- 
racy of my assertions, and to establish his own hypothesis on 
a firmer and more indestructible basis. But since he has 
declined to do so, I must, of necessity, call his attention still 
more closely to the error he has committed in referring the 
subject of dispute to the genus Amphiprora. On reauin, 
Dr. Arnott’s description, which, he will permit me to observe, 
is very vague and without anything specially diagnostic, of 
Apr. Ralfsii, in the last volume of this Journal, p. 91, 
* ¢Trans. Micros. Soc.,’ vol vi. 
+ One of these slides was sent to me by an esteemed correspondent, 
Mr. Roper, and another from Dr. Montgomery, of Penzance. 
t On the 21st of October, 1857. 
