Diatomaceous Sand of Glenshira. 
41 
moniliform, as in many other naviculze, but this character is 
far from being conspicuous. Moreover, the invariable and 
decided colour of the valve distinguishes it from N. granula.ta, 
which is colourless. Neither have I ever seen in N. latisnima 
the produced or apiculate apices of N. granulata. I consider 
N. latissima to have very well marked characters, and the 
aspect of the larger individuals to be entirely peculiar. 
Fig. 4 represents one of the shorter, and fig. 4* one of the 
longer forms of this fine species. (262.) 
5. Navicula quadrata, n. sp. { = N. humerosa^ Breb.) This 
form is allied to the preceding, and is equally frequent in the 
deposit. 
Form rectangular or nearly square, the ends suddenly con- 
tracted to short produced apices. Length from 0*0015" to 
0'005" or even more, the breadth not increasing with the length 
in the longer individuals. The usual length is about 0 0025" 
or 0*003". Striae radiate, much finer than in N. latissima-, 
minutely moniliform, coming nearer to the median line. Fig. 5 
represents an example rather below the average size. 
When I first observed this form, and sent it to de Brebisson, 
he told me that he had then just found it at Falaise, and had 
named it N. humerosa ; but he preferred my name as having 
been the earlier, and as more characteristic. Subsequently, 
Professor Smith referred it to N. granulata,, Breb., with which 
it agrees in form, while it differs from it remarkably in 
striation and aspect. De Brebisson, having found it quite un- 
mixed with N, granulata^ still, I believe, regards it as a dis- 
tinct species.* For this reason, I give it here as such, adding, 
however, that I think it probable that it may prove to be a 
variety, not indeed of N. granulala, but of N. latissima, from 
which it differs, indeed, both in form and in number of striae, 
but which it resembles considerably in general aspect. In my 
paper on Navicula varians,^ I have shown that neither outline 
nor number of striae are to be relied on, in certain cases, as 
specific characters, and I shall take an early opportunity of 
directing attention to other facts of the same kind which 1 
have since observed. I may add that in this deposit there 
occur forms which, both as regards outline and striation, are 
intermediate between this one and the preceding, N. latissima. 
Even as a variety, however, it requires to be noticed and 
figured, in order to give a correct idea of the species as we find 
it. (263.) 
I may here state that all the three forms, iV^. latissima, 
* It appears as such, I find, in Vol. II. of the Synopsis, p. 93, as N. 
humerosa. Of course I shall withdraw my name, and adopt that of de 
Brebisson, to avoid confusion. 
t ' Quart. Journ. of Micr. Science,' No. X., p. 10, Jan. 1855. 
