44 
Dr. Gregory, on the Post-tertiary 
shira sand is particularly remarkable for the occurrence in it of 
several different forms of the same general type, which I figure 
that they may be compared with others from different localities. 
That which I have named, doubtfully, N. Paiidura, is in 
shape panduriform, very deeply constricted in the middle, 
with the extremities nearly triangular, broad, with somewhat 
acute apices. Nodule square ; median line strong, double, 
straight, with two dark lines, parallel to it, and close to it on 
each side, converging at the ends. These lines are shades, 
caused by elevations in the striae, and similar to those in 
N. elliptica, Kutz {ovalis, Sm.), and in JV. didyma. Length 
0'004" to 0*005". Striae coarse, very conspicuous, costate. 
Indeed, had not de Brebisson named his form Navicula, I 
should have called it Pinnularia, as the costae resemble those 
of P. alpina. It will be seen that the next form has the same 
character. (269.) 
12. Navicula iiitida, Sm. ? I have named this form, repre- 
sented in fig. 12, also doubtfully, as no description of the 
species has yet appeared. It is represented in fig. 12. Form 
like that of the preceding, but less deeply constricted, and the 
ends longer in proportion. Length 0 003" or 0"004''. Striae 
not quite so coarse as in the last, costate. I have been re- 
peatedly informed that this is Professor Smith's ]V. nitida, but 
I cannot reconcile this with his definition of Navicula as 
having moniliform, Pinnularia as having costate striae. (270.) 
13. Navicula incurvata, n. sp. This form, Avhich belongs to 
the same group, is a true Navicula, if that generic name imply 
moniliform striation. 
Form approaching to that of the two preceding species, but 
much more gently constricted, narrower in proportion, and 
with the extremities very uniformly rounded. Median line 
straight, with the dark-shaded lines on each side. Striae much 
finer than in the two last, about 30 in 'OOl ", and minutely 
moniliform. It is perfectly uniform in its character, and a 
well-marked species. Length 0-003" to 0*004". (271.) 
14. Navicula splendida^ n. sp. This very fine species is also 
a true Navicula, but still belongs to the same group. 
Form panduriform, much constricted, very broad at the 
shoulders, ends triangular and obtuse. Length 0'005" to 
0*006." Median line straight, nodule square. Striae rather 
fine, compared with the two first forms of the group ; but dis- 
tinctly moniliform ; not reaching the median line, and leaving 
on each side of it a long narrow blank space, which adds to its 
apparent breadth. The aspect of this form, as may be seen in 
the figures, is very different from that of the other forms of the 
group. It is the rarest of them in this deposit, and, as yet, has 
not occurred elsewhere. (272.) 
