P E E P A C E .
T h e siliceous epiderms of the Diatomaceae have, of late years,
furnished the microscopist with a series of objects, not merely
attractive to the general observer, from the elegance of their forms,
but interesting to the more scientific student from the minute
complexity of their structure, whose detection and delineation call
into requisition the exercise of the most patient observation and
the skilful management of the highest powers of his instrument.
Much attention has in consequence been drawn to these minute
organisms, and the want of some English manual, containing a
classified arrangement and description of species, has been extensively
felt. The present work has been undertaken to supply
this want, and owes its appearance to the enterprise and liberality
of the eminent opticians whose names appear on the title-
page. While securing me from loss, these gentlemen have placed
me under no inconvenient restrictions, and have left me at
liberty to render the work, as far as possible, a record of the
facts at present known with regard to the Diatomaceae. So little,
however, has been published upon the subject by English naturalists,
and my views of structure and classification differ so
widely from those of continental writers, with whose works I am
acquainted, that I have found it necessary to make the follownng
pages little else than a record of individual observation. To