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II. — The Markings of Frustulia Saxonica. 
By Samuel Wells, Mass., U.S.A. 
{Taken as read he/ore the Royal Microscopical Society, 1876.) 
It may not be important whether this minute diatom is marked 
with longitudinal lines or not, but if the appearances of such lines, 
which have led to controversy, are to be taken as suitable tests for 
spurious lines, the question becomes one of considerable importance. 
I was formerly of the opinion that these lines resulted from diffrac- 
tion, and in coming to that conclusion I was aided by Dr. Wood- 
ward's article in the ' Lens ' of October, 1872.* Subsequently, with 
better objectives and improved methods of illumination, I changed 
my opinion, and satisfied myself that the longitudinal lines are as 
real as the transverse. In Dr. Woodward's communication to the 
Eoyal Microscopical Society,! he states that he still regards the 
lines as spurious, and enforces his opinion with some of his admi- 
rable photographs. These are arguments very difficult to answer, 
and outweigh the simple statement of many observers to the con- 
trary. I have therefore not thought it useful to attempt to discuss 
the subject until I could support my opinions with arguments of 
the same kind — whether of the same force others may decide. 
In order to guard against the possible charge that I have 
mistaken the coarser forms of the same species (Khomboides) for 
the variety in question, I have selected for the photograph a par- 
ticular frustule already on record, being the identical specimen 
numbered 18 on a Moller's Probe-Platte measured by Professor 
E. W. Morley, whose communication is published in the ' M. M. J.' 
of May last, p. 223. This Probe-Platte is the one marked C by 
him in his table of measurements on p. 226, and on this particular 
frustule he finds the transverse striae to range from 81 '5 to 82*7 
in •001". I think, therefore, it may fairly be called a representa- 
tive frustule of the F. Saxonica, although apparently somewhat 
larger than those selected by Dr. Woodward for his photographs. 
The accompanying photograph f of this frustule, marked A, 
shows the longitudinal lines over the whole surface. I find them 
to be 88 in 'OOl", but do not claim great accuracy in the measure- 
ment. It will be noticed that this frustule is in balsam, while the 
lines are therefore fainter than they would be in a dry mount, yet 
the balsam eliminates the principal cause of the disturbing spurious 
lines. The midrib and margin of this species are quite thick, and 
* Reprinted 'M. M. J.' vol. xiv. p. 279. f 'M. M, J.' vol. xiv. p. 274. 
X The photographs sent, those of F. Saxonica and A. pellucida, rather bear out 
the author's views. They are, however, hardly of sufficient interest to demand 
a Plate ; we have therefore placed them with the other photographs which 
Mr. Wells has sent to us, in the hands of Hon. Secretaries of the Royal Micro- 
scopical Society. — Ed. ' M. M. J.' 
