of Diatomaceous Forms. 
11 
In a gathering from the vicinity of Oban I found several ; 
one very near the original oval form, but with flattened apices, 
and a slight tendency to constriction just within them. These 
last, which closely resemble Pinnularia oblonga, shortened, 
and rather broader in proportion, are frequent in a Norfolk 
gathering sent me by Mr. Bleakley, in which occur also 
several others. 
The Oban gathering contains also various other forms of 
this group, one of which has precisely the form and size of 
Pinnularia acuta, and as that species occurs along with it, the 
two forms are easily compared and distinguished. Here also 
occur forms approaching nearly to that of Pinnularia pere- 
grina, although in a purely fresh-water gathering. 
In another similar gathering from a bog in Ayrshire, there 
is abundance of a form not to be distinguished from P. pere- 
grina, along with others of the outline of P. acuta, P. radiosa, 
&c. 
I now began to suspect that these forms might all belong to 
one species, for on close inspection I found a very large num- 
ber of intermediate or transition forms. I, therefore, named 
the supposed type Navicula varians^ and continued to search 
for its modifications. 
In the Glenshira sand, although not very abundant, it ex- 
hibits all the forms as yet enumerated, but chiefly those which 
have an outline allied to that of Pinnularia gracilis, but twice 
or thrice as large, and to that of P. peregrina. These forms 
and several others I have since found abundantly in the recent 
mud or sand deposited by the Dhu Loch, near the mouth of 
the Glenshira, the lake which when at a higher level in the 
valley, deposited the Glenshira sand described in the last 
number of this Journal. 
Having received from the Rev. Professor Smith, in Sep- 
tember, a slide, of fresh-water origin, in which Navicula 
varians, of the type of Pinnularia peregrina, was very abun- 
dant, I begged Mr. Smith to examine the form, which he 
found, as in all the other types of N. varians which he had 
seen, to have moniliform striEe. He then extended the inquiry 
to the tjipical Pinnularia peregrina, and found that it also had, 
at all events in many instances, moniliform striae. From this, 
I concluded, that in all probability Pinnularia peregrina was 
at all times only a type of ]V. varians. I believe Mr. Smith 
intends to change the generic name oi P . peregrina to Navicula. 
It seems to me in the highest degree probable, that Pinnu- 
laria ohlonga is nothing else than another type of N. varians. 
For the form (fig. 1) does not differ from P. ohlonga, except 
in length, every other detail being identical in the two forms : 
