8 DONKIN, IN REPLY TO WALKER-ARNOTY. 
all these last mentioned species occurred in Mr. Ralfs’ Pen- 
zance gathering. Repeated examinations, however, have con- 
vinced me that this is an error, as Pl. rectum is the only form 
T can detect. It is necessary to state that my Pl. Wausbecku 
is the variety of PJ. balticum, figured by Professor Smith im 
his ‘Synopsis ;’ but I am at a loss to understand why he con- 
sidered it as such. There is certainly nothing more than a 
generic resemblance between the two forms as regards outline, 
colour, and the relation of the median line to the margin, 
while the strie of Pl. Wausbeckii are considerably finer than 
those of Pl. balticum. 
I confess myself at a loss to understand Dr. Arnott’s 
hypothesis, which enables him to look upon the two members of 
my new genus Towonidea as accidental or twisted conditions of 
Pl. strigosum, angulatum, and estuarii, produced by a peculiar 
process. This assertion I do not credit; and nothing short 
of actual observation, I feel assured, will satisfy any partial 
inquirer as to its validity. It would be well, therefore, were 
Dr. Arnott to state whether he has seen such a phenomenon 
take place, and if so, to describe it. For undoubtedly any 
physiological or pathological process which can effect so great 
a change, not only in the general outline, in the relative 
position of all the parts, and in the cellular structure of the 
siliceous valve of the Diatome, must of necessity be a most 
singular one, and its demonstration by Dr. Arnott cannot fail 
to attract that interest which falls to the lot of every important 
physiological discovery. 
These remarks, I trust, will be amply sufficient to show that 
Dr. Arnott has, on very insufficient grounds and in no liberal 
manner, accused me of creating “‘swpposititious’”’ species out of 
mere varieties, and thereby encumbering science with useless 
and unmeaning names. As to the regret which he expresses 
at what he calls “rushing into print,’ without making myself 
acquainted with what others are doing, I must observe, in 
reply, that while, in my paper, I have studiously avoided any 
attempts at plagiarism by adopting as my own the published 
discoveries of other observers in the same field, I was at the 
same time unable to command the supernatural assistance of 
an Asmodeus, to unveil to my observation their present 
doings and cogitations. It is certainly true, as stated by Dr. 
Arnott, that I had described certain species which had 
previously been found by M. De Brebisson at Dines. Of 
this fact, however, I was entirely ignorant until a few days 
prior to its publication; when M. De Brebisson himself 
sent me some slides, mounted from his gathering made in 
that locality, in order to ask me whether the new species 
