Diatomaceous Sand of Glenshira. 
83 
48. Synedra Baculus, n. sp. This form is not at all rare in 
the deposit, and I cannot refer it to any of the Synedr(S in 
the ' Synopsis/ vol. i. It is certainly not S. superba. 
Form linear, rather narrow, very nearly of equal width 
throughout on the S. V. ; ends obtuse; F. V. rectangular. 
The valve is transversely striated. Striae rather conspicuous, 
and traversed hy faint longitudinal lines. Length from 
0-01" to 0-018" or even 0-02". It is represented in fig. 54 (300.) 
I have now to mention a few forms, which I do not venture 
to name, partly from not having yet been able to study them 
fully, and partly because I have not been able to refer to all 
the works I wish to consult. One or two of them may pro- 
bably prove not to be Diatomacem . 
49. Orthosira or Coscinodiscus ? This disc, represented in 
fig. 48, is frequent in the deposit, and I have not been able to 
trace any view but that which is figured, or consequently to 
ascertain whether it be an Orthosira, which it may be, or a 
disc of some other genus, or finally a discoid diaphragm or 
dissepiment, belonging to an Orthosira or some similar form. 
Diameter from 0*001'' to 0'6025''. Margin transversely 
striated. General surface marked with very fine short lines, 
apparently devoid of any regularity of arrangement. These 
are very difficult to resolve ; but it is easy to see, all over the 
surface, small distant puncta, scattered sparsely, without 
arrangement or symmetry. The disc is convex. (301.) 
50. Coscinodiscus or Actinocyclus ? This disc is not very 
rare, but less frequent than the last. The same general re- 
marks apply to it. It will be figured in connection with our 
communication on the Clyde forms, want of space having 
compelled its omission here. 
Diameter, as in the preceding case, from 0*001" to 0*0025", 
but often as much as 0*003". Colour brown. The whole 
blue, pale blue, greenish blue, green, and yellowish green; and, in a few cases 
brown, passing from brown to purple. I have also seen one or two indivi- 
duals of a buff colour, exhibiting the angular blanks which characterise the blue 
ones. On the other hand, E. sparsus is always brown, buff-coloured or colour- 
less. When tbe two forms occur together, E. sparsus is seen to be in general 
much larger and much flatter, and it does not exhibit the angular blanks, 
which, as I suspected, are the results of the arrangement I have described, 
in E. Ralfsii, where the rays and granules are both closely set, and the 
granules larger. The largest examples of E. sparsus are in general the 
least coloured, probably because the granules are even less closely set than 
in the smaller discs, and the angular blanks are entirely absent. Whether 
these differences, producing so great a difference of aspect, be specific or 
not, I must leave to others to decide. At present, I am at a loss to account 
for the fact, that two discs may occur, of the same size, and both buff- 
coloured, one of which shows the angular blanks, while the other exhibits no 
blanks whatever.) 
VOL. V. h 
