Diatomaceous Sand of Glenshira. 
87 
but seldom. This is strongly in contrast to the results here 
described^ where one deposit^ in great part of marine origin^ 
has yielded more than sixty new forms, the great majority 
of which have not yet been fonnd elsewhere. 
This leads me to observe_, that while some dislike the 
labour of searching for forms in such complex mixtures as the 
deposit before us, I cannot help thinking that it is worth 
while to undergo this labour. Had we waited until the most 
curious of these forms should have occurred in a comparatively 
unmixed or pure state, many years must have passed before 
they became known. And although we cannot, for example, 
make sure of finding in every slide specimens of such remark- 
able forms as Amphora obtusa or Amphora Grevilliana, and 
the others of that singular group, yet, to obtain a knowledge 
of such a group, we ought not to grudge the trouble of 
mounting a few extra slides. The Glenshira Sand, even when 
purified as much as possible, and sorted into densities, is 
indeed loaded with mica in the coarser, and a very com- 
plex mixture of forms and mica in the finer densities. 
But the results speak for themselves, and I am very far 
from regretting the time and labour I have devoted to the 
investigation. 
In conclusion, I would mention that the Glenshira Sand 
will supply observers not only with the new forms, except, 
perhaps, two or three that are very scarce, but with fine 
specimens of many known forms which are not always easily 
procured elsewhere. Of these I may name Amphitetras ante- 
diluviana, the strongly emarginate variety being frequent, 
the square one less so ; Stauroneis pulchella, of the largest size, 
extending to 0 01" or more, and varying much in form; (this 
is Stauroptera aspera of Ehrenberg;) Coscinodiscus radiatus, 
fine, varying much in the size and aspect of the cells, and 
possibly including more than one species. Coscinodiscus 
concinnus, mentioned in the ^ Synopsis,^ vol. ii ; Navicula 
convexa, very fine and large; N. Jenneri, extending to 
O'OOS" or more in length; Pinnularia megaloptera, Ehr., of 
which P. lata, Sm., is most probably a short variety. This 
form occurs so long as 0'006, but more generally 0*004 to 
0*005. It is, however, rather scarce. Epithemia Hyndmanni, 
very fine and large; Coscinodiscus excentricus ; Eupodiscus 
crassus ; Campylodiscus Hodgsonii, this is rather scarce ; Suri- 
rella fastuosa, large and fine, sometimes very large and con- 
stricted in the middle, in which case it much resembles >S^. 
lata, and, it is possible, may pass into that form. Synedra 
superba ; Nitzschia bilobata, rather scarce. Amphiprora vitrea, 
very fine ; Amphiprora elegans, sometimes very large. Na- 
