Diatomaceous Sand of Glenshira. 
79 
eight prongs, forming spaces_, which differ in shape from the 
different origin of the boundary lines. Between the inner 
margin and the outer one, the narrow space is transversely 
striated. Diameter of disc about 0-027". (294.) 
43. Tryblionella apiculata, n. sp. In my former paper I 
figured T. constricta, which name I find has been adopted by 
Professor Smith. I had also observed this one, but had not 
then satisfied myself that it was distinct. Having since then 
found it in recent gatherings, alone, that is, without the 
shorter T. solmformis or constricta, I am inclined to regard 
it as distinct, especially as I understand that Professor Smith 
thinks that I had included two forms under T. constricta. I 
may here add that Dr. Greville has found in the Trinidad 
sand, a short, broad, slightly constricted and apiculate form, 
which seems to be a Tryblionella, allied to these. This last I 
have also since observed in the Glenshira Sand, though 
perhaps a little smaller. It is possible that all three may be 
forms of one species. Pig. 43 represents T. apiculata. 
Form linear, narrow, slightly constricted in the middle; 
extremities apiculate. Keel strongly marked in many speci- 
mens, strise fine but distinct, about 45 in 0 001". Length 
0"0015" to 0*0017". The striation is peculiar, for in many 
specimens it is easy to see not only transverse, but also 
oblique striae. This character was first observed by Dr. Gre- 
ville in the Trinidad form, so far as I know, but I have since 
observed it in all the forms, though not in every individual. 
These forms require a more full investigation than I have 
been able to give to them. That here figured, or one appa- 
rently the same, occurs in a recent gathering from the 
Cumbrae Isles in the Clyde, with only fresh- water forms, but so 
near the sea, that the Tryblionella may possibly be marine. 
In Dr. Greville^ s Trinidad sand, both marine and fresh-water 
forms occur. (295.) 
44. Nitzschia distans, n. sp. This form is frequent in the 
deposit ; want of space, however, has prevented its being given 
on this plate. 
Form of the F. V. rectangular, the corners rounded. In 
some specimens I observe a small expansion, analogous to that 
in N. spathulata, but smaller, on each side near the extremities. 
This is not seen in the figure, having probably been absent 
from the individual figured, or not seen by the artist from its 
transparency. The markings are unusually distant, hence the 
name. They appear to be almost moniliform, and, under a 
high power, appear as if constricted in the middle, so as to be 
nearly divided, while faint longitudinal lines appear to pass 
from one bead to that opposite to it in the next transverse 
