NEW FORMS OF MARINE DIATOMACE.E. 535 



very great weight with all students of the Diatomaceae. 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 Greville has made of the forms which I 

 have described, and to the signal success with which Mr Tuffen 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 Diatomaceae 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 thestriation, 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. Hi., p. 10), and in this paper I 

 have done so partially in Navicula Lyra, Nav. Smithii, Amphora Proteus, and 

 Amphora lasvis. Such forms as iV. elliptica, N. didyma (which I have in part illus- 

 trated in my last paper on the Glenshira Sand), N. Crdbro and P. Pandura, for 

 example, and even N. 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 Smith, 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, 



