12 Gregory, on a remarkable Group 
and although I cannot say that I have seen the moniliform 
character of the striae either in fig. 1, or in P. ohlonga^ I believe 
that this has been seen in the former. If so, any one who 
compares the two forms which occur together, both in the 
Oban gathering, and in Mr. Bleakley's gathering from Norfolk, 
will see that the latter can hardly fail to exhibit the same 
character. I have not myself been able as yet to attempt the 
resolution of these striae with any refinement of appliances, 
and therefore I must leave this point for future examination. 
I have still to notice one more type, which I first observed 
in a gathering from Lochleven, where it is very scarce, but 
which is frequent in a second and distinct gathering of Mr. 
Bleakley's from Norfolk. It is rather small, and either of a 
short and very broad oval form, or absolutely discoid, but has 
all the characters of the group. It is seen in fig. 17. At first 
I supposed it to be distinct, but I have since been led to 
suspect that it is only a form of the group I have described. 
This, however, is by no means certain. On the one hand, 
it seems to be certainly a Navicula, although in this point of 
view its orbicular form is very remarkable. It also varies to 
ovals of different proportions, and it has exactly the striation 
of the first observed form of N. varians (fig. 25), to which, 
indeed, in shape, the oval varieties approach very closely. 
On the other hand its variations are, so far as I have yet seen, 
confined within rather narrow limits ; and its form is so striking, 
that I had named it at one time Navicula orbicularis. Since 
the preceding sentences were written, I have been informed 
that this species was some time since named by Mr. Smith 
Navicula scutelloides. So far as I know, it has only occurred 
as yet in the two localities I have mentioned ; namely, Norfolk 
and Lochleven. 
We have now mentioned most of the observed types of N. 
varians, so far, at least, as they present the characteristic stria- 
tion and aspect ; and although all the forms I have named 
may not be found to belong to it, yet it appears that there 
exists a large group, characterised by a very peculiar aspect 
and striation, the number of striae varying only from about 14 
in '001" in the larger to 18 in "001" in the smaller forms, 
the usual number being 16. 
This group seems to include several which have been con- 
sidered as distinct species, such as Pinnularia (^Navicula) 
peregrina, and other forms, referred to Navicula semen, N. 
rhyncocephala, Pinnularia gracilis, P. radiosa, &c., although 
in these three species the normal striation is 26 in "001". 
But there are even more of the forms of this group which are 
und^scribed, such as the round and oval forms ; that which 
