64, MEMORANDA. 
and, as I had concluded, from the imperfect specimens I had 
seen, attains a length of from 0:015 to about 0°02, which, 
for a Diatom, is gigantic. I had previously noticed a frag- 
ment of it in arecent gathermg made by Professor Smith, and 
he had himself subsequently found it frequent in Cork harbour. 
The first observer, however, was Professor Bailey, of West 
Pomt, New York, who had found it still larger on the 
American coast, which I was not aware of till long after my 
observations on the Glenshira sand were made. 
*‘The third observation I shall here record is, that in these 
dredgings I found, in sufficient abundance, several very 
curious forms which had occurred in the Glenshira sand ; 
but the description and figuring of which I had postponed, 
because either they were so scarce that I could not obtain 
good specimens, or, being only found in a fragmentary, de- 
tached, or imperfect state, I was quite at a loss to determine 
their true nature and position. I think I may say that in 
every such case I have been enabled, by the study of the 
new materials, to understand the nature and structure of 
these obscure or doubtful forms, and to establish them as 
new and distinct species. I have also been enabled to under- 
stand better several of the forms which were figured in my 
former papers, and to correct some errors which had crept 
into these. 
“J need not here give a list of the forms just alluded to, 
as the will be included in that of the new forms to be de- 
scribed. In that list I shall mark them with a G, to indi- 
cate that they were first noticed in the Glenshira sand. 
“Lastly, i the new materials I have found a large 
number of entirely new and undescribed species. I may 
here mention, that although a good many fresh-water 
forms do occur in these dredgings, as must, indeed, be | 
the case, since the Clyde and all its tributaries bring 
down such forms, yet the new forms in question appear 
to be all of marine origin. They are, in general, much 
too abundant to have been derived from any other 
quarter, whereas the fresh-water forms among them are 
much scattered. It is proper also to state, that although 
all these forms are, to the best of my belief, new to Britain, 
yet a few of them have been described by Ehrenberg in some 
of his numerous works, and also by De Brébisson. The 
great majority, however, have not anywhere been figured ; 
not, at least, in any works accessible to me.” 
