Diatomaceous Sand of Glenshira. 
37 
as a British form in Vol. II. of Smith's Synopsis. I have 
found in Glenshira several forms of this kind, differing only 
in the number of septa, which varies from 7 or 8 to 14 or 
16. I observe in Pritchard's Animalcules, that Ehrenberg 
makes a species of each number of septa ; but to judge by the 
aspect of these forms in Glenshira, they are all of one species, 
which I have named duodenarius, because 12 is about the 
average of the septa in those I have seen there. No. 250, 
Navicula Pandura, was last year figured by De Brebisson as 
occurring at Cherbourg. I mark it with a query, because it is 
doubtful whether it may not be the same species as N. nitida^ 
Sm., (named in my former list,) and also because I have 
great doubts as to either of these forms being correctly named. 
They belong to a very striking group, in which the Glenshira 
sand is somewhat rich, and which I shall have presently to 
consider more fully. 
Of No. 247, Navicula Hemiedii, I give a figure, because very 
fine specimens occur in this deposit, and the form has not yet 
been figured, though it will be described in Vol. II. of Pro- 
fessor Smith's Synopsis. The two OrthosircB are also new 
forms ; O. spinosa having been found in Braemar by Drs. 
Greville and Balfour, and in Auvergne by Professor Smith, 
and figured both by Dr. Greville and Professor Smith ; and 
O. mirabilis having been found last summer in Wales by Mr. 
Okeden, but not yet figured. I may here mention, that I had 
observed and sketched both, in my earliest explorations of the 
Glenshira sand, fully three years ago ; but from the number 
of new forms, I was compelled to postpone the study of them, 
and had not been able to resume it when the naturalists above 
named discovered them. But before the account of O. spinosa 
had appeared, I had again found both forms in three or four 
South American soils. I mention this here, because my ob- 
servations on these soils have led me to doubt whether O. 
mirahilis be not an abnormal state of O. spinosa. 
My reasons for thinking so are: 1. That in all the localities 
in which O. mirabilis occurs, it is accompanied by O. spinosa. 
2. In the Glenshira sand and in the American soils, I was un- 
able to find any discoid or end view, or diaphragm, which I 
could suppose to be that of O. mirabilis, except that of O. 
spinosa; and I believe that Mr. Okeden has been equally 
unsuccessful. 3. I found one cylinder, one-half of which had 
the peculiar markings of O. mirabilis, namely, two series of 
curved or sigmoid lines, decussating and crossing the cylinder 
transversely ; while the other half had all the characters of 
O. spinosa. 4. In no specimen of O. mirabilis have I seen 
any appearance of the usual septa, so strongly marked in 
e 2 
