54 
KoPEEj on the genus Licmophora. 
whicli present constant and strongly marked peculiarities, 
a vast number of the forms included in their genera, in the 
absence of authentic specimens, are now quite unknown, and 
can neither be determined by their specific characters or 
figures. The difiiculty thus presented to the English ob- 
server may be estimated by the fact stated in the preface to 
Professor SmitVs ^ Synopsis,^ that, out of the 224 species 
included in his first sub-tribe, not more than twenty had 
been previously recorded by native observers, and of the 
remainder a very large proportion are only doubtfully to be 
referred to the outline figures of Ehrenberg and Kiitzing. 
The appearance of Professor Smithes researches at once 
obviated the great difficulty the English diatomist had to 
contend with ; and afibrding a sure foundation to start from, 
brought a host of observers into the field, attracted by the 
great beauty of the hitherto neglected frustules of the tribe, 
by the abundance with which they are found in almost every 
locality, and especially to the field thus ofi^ered by a more 
careful examination of marine and foreign collections for 
the description of new species or varieties of those already 
known. 
The great advantage Professor Smith's work ofi'ers over 
that of all his predecessors, consists in the determination 
he formed, and to which, except in a few cases, he adhered, 
not to admit species unless he had an abundant supply of 
material for investigation ; in the beauty and accuracy of Mr. 
TuflFen West^s illustrations ; but chiefly to his own authentic 
slides being made available to the public for nearly all the species 
described in the ' Synopsis.'' The value of his work, there- 
fore, as a basis for further observation, is far greater than 
that of any of his predecessors; and though, had his life 
been spared, he would doubtless have availed himself, in 
another edition, of the extended researches he originated, to 
modify some of his species, and probably also some parts 
of his classification — still, the greater part of those species 
he has included in the ' Synopsis^ are well authenticated, can 
be readily recognised, and will form a sure ground work for any 
future writer on the subject. 
That in a first attempt to describe our native species of 
these minute and lowly organized forms of life, so few errors 
should have occurred is truly remarkable, when it is remem- 
bered how little was known of the variations arising from 
habitat ; of the influence of the temperature of the water, and 
the efl'ect of salt, brackish, or fresh water on the form and 
marking of the frustules ; of the astonishing rapidity with 
which slight structural peculiarities might be perpetuated by 
the process of self-division ; and that, except in a few genera, 
