40 
Dr. Gregory, on the Post-tertiary 
figured in the Synopsis, Vol. I., and I was at the time little 
acquainted with it, 1 was at first inclined to adopt this view. 
But a further examination of both forms has satisfied me 
that they are distinct. N. firma has, even in balsam, a 
strong brown colour ; its striation is coarser, and far more 
conspicuous, and is also slightly inclined ; and it forms 
several well-marked varieties, which have been described and 
figured by Ehrenberg as distinct species, such as JV. dilatata, 
N, amphigomphus, and others. Now, so far as I can see, 
N. maxima exhibits no other varieties than those here figured, 
which I give for the purpose of comparison. Moreover, while in 
N.Jirma^ in all its forms, we have a side line on each side of 
the median line, N. maxima has usually two such lines on 
each side. Lastly, both forms occur in this deposit, and are 
easily distinguished by their general aspect, even under a low 
power. (225.)* 
3. Navicula Hennedii, Sm. I give a figure of this beautiful 
species, because no figure of it has yet been published, and 
because the finest specimens I have seen occur in the Glen- 
shira sand. As it will be fully described in the Synopsis, 
Vol. II., I need only say here, that fig. 3 represents a very fine 
one, although I have a specimen one-half larger even than 
this. (247.) t 
4. Navicula latissima, n. sp. This is another very fine 
species, which occurs very well developed in our deposit. 
Form very broadly elliptical, with very obtusely acuminate 
apices, having usually a very slight constriction before the 
extremities. The sides are occasionally parallel in the middle. 
Length from 0-002" to 0-005", or even 0 006". Some of the 
shorter individuals, from the great breadth, are nearly or- 
bicular. Nodule very large, median line doubly conical, the 
bases of the cones meeting at the nodule. This appearance is 
due to the striation, which does not reach the middle, and re- 
cedes farthest from it near the central nodule. Striae rather 
coarse, finely moniliform, highly radiate, and not reaching the 
true inner median line. Colour of the valve, in balsam, a 
strong straw yellow, occasionally light brown. 
I understand that some are disposed to refer this form to 
N. granulata, Breb,, which, as I stated in my former paper, 
also occurs here. But I cannot do this ; for in N. granulata, 
not only are the striae much less numerous, even though it is a 
considerably smaller form, but they are composed of large 
granules, so distant as to give a special character, from which 
the name is taken. In N. latissima, the striae are indeed 
* So numbered in Part I. 
t So numbered in the list of known forms, given at page 34. 
