476 PROFESSOR GREGORY ON 
Before going farther, I have to remark, that two of the forms in the first list 
above given, namely, Campylodiscus Horologium and Himantidium Williamsoni, 
which had only been found by Professor WitL1amson, who detected them both in a 
dredging made by Mr Bartz on the coast of Skye, in which they were very scarce 
indeed, have occurred abundantly, the former in one of the Loch Fine dredgings, 
and sparingly in some of the others, the latter in another of them, and, though 
less abundantly, yet frequent in nearly all the Clyde materials. We shall see 
that Himantidium Williamsoni, which Professor Smrru had referred doubtfully to 
that genus, not having been able to see more than the front view of it, is really no 
Himantidium ; the side view, which is very abundant in one of my dredgings, hav- 
ing characters quite incompatible with the genus Himantidium. On this account, 
I shall refer to it among the new forms which I have to mention. I have found it 
a matter of very great difficulty, if not impossible, to refer it to any of the genera 
in Smirn’s Synopsis. I may here add, that Synedra undulata, which I had recog- 
nised in the Glenshira sand, but which had never occurred entire in that de- 
posit, is frequent in the first material from Lamlash Bay (Professor ALLMAN’s), 
where it occurs quite entire in more than half of those I have seen, and, as I had 
concluded, from the imperfect specimens I had seen, attains a length of from 
0015 to about 0:02, which, for a Diatom, is gigantic. I had previously noticed a 
fragment of it in arecent gathering made by Professor Smrru, and he had himself 
subsequently found it frequent in Cork harbour. The first observer, however, 
was Professor Baitry, of West Point, 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, be- 
cause either they were so scarce that I could not obtain good specimens, or, 
being only found in a fragmentary, detached, 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. 1 have also been enabled to understand better 
several of the forms which were figured in my former papers, and to correct 
some errors which had crept into these. 
I need not here give a list of the forms just alluded to, as they will be in- 
cluded in that of the new forms to be described. In that list, I shall mark them 
with a G, to indicate that they were first noticed in the Glenshira sand. 
Lastly, in the new materials I have found a large number of entirely new and 
undescribed species, which I shall now proceed to enumerate. I may here men- 
tion, that although a good many fresh-water forms do occur in these dredgings, 
