NEW FORMS OF MARINE DIATOMACEX. 535 
very great weight with all students of the Diatomaceze. I have further to thank 
Mr Roper for many useful hints, and for the use of some very accurate drawings 
of forms observed by him, in many cases identical with those I had myself de- 
scribed. 
It is impossible to do full justice to the scrupulous accuracy and to the ar- 
tistic beauty of the figures which Dr Grevitie has made of the forms which I 
have described, and to the signal success with which Mr Turren West has en- 
graved them. I can only say that I have seen no figures of this kind equal to 
them in these respects, and that the chief value of communications like the pre- 
sent is derived from the presence of good figures. Without figures, descriptions 
are apt to be misunderstood, and inferior figures tend, more than any other 
cause, to lead observers to multiply species unnecessarily. Those who are in 
the habit of studying the Diatomacez will agree with me, that a large proportion 
of the figures in some works on the subject are worse than useless, and lead to 
hopeless confusion. 
There is another point on which good figures throw much needful light. In 
many species, though by no means in all, the shape, as well as the size of the 
forms, and even the striation, all vary to a great extent. In such cases, it is 
most important that every author should figure a sufficient number of selected 
forms, to show the real extent of the species. These variable species ought to be 
thus treated individually, by which means many existing species would be got 
rid of and reduced to a smaller number. I have attempted something of the 
kind in Navicula varians (Trans. Mic. Soc., vol. iii., p. 10), and in this paper I 
have done so partially in Navicula Lyra, Nav. Smithit, Amphora Proteus, and 
Amphora levis. Such forms as WN. elliptica, N. didyma (which I have in part illus- 
trated in my last paper on the Glenshira Sand), NV. Crabro and P. Pandura, for 
example, and even WV. Smithii, besides others in different genera, require much 
fuller illustration than they have yet received. 
Finally, I wish it to be understood, that in describing so many new species, I 
make no pretensions to deciding authoritatively on disputed or doubtful points. 
My sole object is to bring under the notice of observers, the forms which I meet 
with. To do this, I must needs give them names, and in this respect I endeavour 
to be as accurate as I can. I observe that Professor Smiru, in his last paper in 
the Annals, objects to the establishment of new species, unless the specimens are 
frequent. But although I have given, as distinct species, some forms which are 
rare, I have not done so till after I had examined and compared many specimens of 
each, except in one or two cases, such as Coscinodiscus umbonatus, where the form 
is so striking and well-marked that even one specimen suffices. 
If we confine our attention to one or two slides, then, indeed, rare forms can 
not be sufficiently studied. But in the researches made in connection with this 
paper, I have explored at least 1000 slides, most of them twice, many three times, 
