Diatomaceous Sand of Glenshjra. 
81 
47. Eupodiscus sparsus, n. sp. In my former paper 1 
figured^ under the name of Eupodiscus Ralfsii (5, but doubt- 
fally^ a fine disc^, wbich is frequent in the coarser densities of 
the Glenshira Sand. I pointed out that^ although in some 
points agreeing with E. Ralfsii, as I had seen it^ (for no de- 
scription of that species had yet appeared^) it yet differed from 
it in the absence of the peculiar elongated angular blank 
spaces^ which in E. Ralfsii are scattered over the surface. 
Since then, I have examined many fine specimens of both, as 
both are frequent in the coarser densities, and I find that 
E. Ralfsii appears almost invariably blue or purple when seen 
with a low power, such as the two thirds, or even the half, and 
sometimes even with the quarter or one fifth. These blue 
discs of E. Ralfsii always showed the angular blank spaces. 
On the other hand, E. sparsus, as I call, provisionally, the 
new disc, is never blue, but always buflP-coloured, or brown, 
or occasionally colourless, even under the low powers. In 
many specimens, no blanks whatever occur ; in some, oc- 
casional blanks appear, but look like the efiPects of injury. 
The figure in my former paper gives a very good idea of 
the general aspect of E. sparsus, but I must add, that in that 
individual, the granules of which the rays are composed are 
set much closer than is often the case. In this particular a 
good deal of variation is observed. 
On a close inspection of the more sparsely grained discs, I 
observed a very curious and beautiful structure, which I have 
found, in great perfection, in the rather small disc represented 
in fig. 47, which is most accurate. 
In this disc, the diameter of which is 0'0019", there are 
twelve principal and equidistant rays formed of round dots, 
not at all closely set. Of such rays, in the common size of the 
discs, diameter 0 003" to 0*0035", there are usually eighteen. 
Between the twelve principal rays, which meet in the circum- 
ference of a small circle, formed round the centre by the ter- 
minal dots of these rays, are twelve shorter rays, which stop 
short, as far from the circumference of the central small 
circle, as that is from the centre. On each side of these 
shorter secondary rays are three similarly dotted lines (in the 
larger discs four such lines), which are not rays, but are 
strictly parallel to the secondary rays on each side of which 
they lie, and of course, in each of the twelve primary segments, 
parallel also to each other. 
In consequence of this very peculiar arrangement, it is 
obvious that the lines, parallel to the secondary rays, cannot 
reach the centre, if produced, nor can they meet the secondary 
rays, but in that case would meet the primary rays at a very 
