NEW FORMS OF MAEINE DIATOM ACEM. 533 



is mixed with S. undulata ; and I know of no distinction beyond that of the ab- 

 sence of undulations on the margin, unless it be that the strise in S. Hennedyana 

 are perhaps a little finer than in S. undulata. Even of this I am not sure. 

 But the figures, which are very accurate, will enable the reader to form his own 

 conclusions. 



Such are the results obtained, up to this time, by the examination of these 

 11 gatherings from the Firth of Clyde and Loch Fine, 10 of which are true dredg- 

 ings, while the 11th is derived from Corattina officinalis, to which a good many 

 Diatoms have adhered. 



From the remarkable analogy between the Glenshira Sand and these gather- 

 ings, we may regard it simply as another dredging, the marine forms in which 

 have been derived from Loch Fine. I have shown that the period at which it 

 was deposited has not caused any material difference of composition, and that we 

 may say, in general, that it does not differ more from the recent dredgings than 

 they do from each other. 



Considering, then, all as supplying us with existing forms, we are struck with 

 the unexpectedly large number of undescribed species which this exploration of 

 the waters of the Clyde, though very limited in the area whence the materials 

 were derived, has yielded in a short space of time. 



It is worthy of notice, that the great majority of these new forms are not 

 only new as British species, but have not been observed elsewhere, although 

 Ehrenberg and Bailey have both described many rich marine gatherings from 

 different parts of the world. 



This proves that the existing stores of marine Diatoms have not yet been by 

 any means fully explored. It is therefore highly desirable that dredgings or 

 soundings from all seas and estuaries, and from every part of them, should be 

 procured and carefully searched. From what has been already recorded, as well 

 as from the results here given, it appears that estuaries and harbours, or other 

 localities near the coast, are likely to be the richest in Diatoms, perhaps from the 

 comparative shallowness of the water. But the conditions of the distribution 

 of these organisms in the sea, and of the accumulation of their indestructible si- 

 liceous shells, are not yet known with certainty. Thus, while every one of these 

 Clyde dredgings proved more or less rich in Diatoms, I have found several from 

 the Long Narrows, in the Firth of Forth, kindly given me by Dr Hector, to be 

 very poor in comparison, and indeed not worth the trouble of mounting. And 

 while Bailey has found many interesting forms of this class in soundings from a 

 depth of 1700 fathoms, and even of 2700 fathoms, in the Kamtschatka Sea, a num- 

 ber of Atlantic soundings, from depths varying from 85 to 2000 fathoms, which, 

 by the kindness of Professors W. Thomson and Allen Thomson, I was allowed to 

 see, contain indeed Foraminifera and Polycystinese, but are almost entirely desti- 

 tute of Diatomacese. Yet Bailey has found Diatoms in Atlantic soundings from 



VOL. XXI. PART IV. 7 D 



