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 Williamson, who detected them both in a 

 dredging made by Mr Barlee 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 Smith 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 Smith'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 AllmanVi, 

 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 

 0-015 to about - 02, which, for a Diatom, is gigantic. I had previously noticed a 

 fragment of it in a recent gathering made by Professor Smith, and he had himself 

 subsequently found it frequent in Cork harbour. The first observer, however, 

 was Professor Bailey, 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. I 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, 



