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the manner I have described, the splendid form Navicula 
Coquedensis having been obtained in the flakes floating on the 
surface of a pool. 
The gatherings made in the rivers Coquet and Breamish, 
both mountain streams flowing from the Cheviot range, bore 
a striking resemblance to those from several localities in the 
North of Scotland, containing in abundance several of the 
species found in them, as described and figured by the late 
Professor Gregory in this Journal. 1 Amongst these I may 
mention Navicula cocconeiformis , Greg., N. bacillum Ehr., N. 
nodosa, Ehr ., N.mtegra, Smith; Stauroneis ovalis, Greg., and 
Surirella tenera, Greg., besides two beautiful forms hitherto 
only found as British species in Ireland, namely — 
“ Surirella Caledonica, Ehr. ( S . turgida , Sra.) and Cymato- 
pleura plicata, Ehr. (C. Hybernica, Sm.), the former in con- 
siderable abundance. 
The invention of the binocular microscope by Mr. Wenham, 
has introduced a most important aid to the study of the 
Diatomaceae, inasmuch as it enables us to obtain a correct 
knowledge of the form and construction of the silicious 
frustule and its valves, previously impossible with the 
monocular instrument. What a striking impression is pro- 
duced in viewing for the first time under the binocular a 
valve of Heliopelta. How very different the configuration of 
this truly beautiful species really is, from the illustration of 
it, as seen by the monocular, given in the plate forming the 
frontispiece to Dr. Carpenter’s valuable treatise on the 
microscope. The same may be said of many other species, and 
indeed of whole genera. I shall merely instance another. 
Hyalodiscus subtilis is described amongst test objects in the 
work just cited, p. 183, as being of a discoid form, and 
having markings which radiate in all directions very much 
like those of an engine-turned watch. Mr. Ralfs, too, whose 
accuracy as an observer is sufficiently well known, says of 
the genus Hyalodiscus : — “ Its flat disc will distinguish it 
from Podosira” 2 Now the fact is that the valve of Hyalo- 
discus subtilis is hemispherical, approaching indeed to conical, 
not a flat disc as it appears to be under the monocular ; while 
the markings, seen radiating in all directions, are optical 
illusions produced by the impossibility of getting into focus 
at a time, under a high power more than a narrow zone of 
the hemispherical valve. Numerous other examples might 
be adduced to show that the monocular microscope with its 
flat field is so unadapted to the study of the diatomaceae, and 
1 Vol. iv, p. 1 ; pi. i, 1856. 
3 ‘Prit. Inf.,’ p. 814. 
