72 THE MICROSCOPICAL NEWS. 
ceous deposit (Monteroy, U.S. A.); but in my case, the hexagonal 
disc was in the interior of the “ frustule,” while the outer consisted 
of a thin plate, with an areola in the centre of each hexagon. 
Decidedly not an opening! as the definition given by objectives 
I in. to ;'g of an in. immersion, and ;), ditto, gave a different aspect 
through the areole than the field outside the valve.* Fig. 26. 
They are considered by M. Pring as openings! He also states. 
that Zrinacria Regina was in the same way found to be crowded 
with small circular apertures! as was evident in the fractures, 
which had the same aspect as those of Coscinodiscus. I also 
examined Z: Régina and excavatus, stictodiscus, and others from 
the Jutland slate, and came to the conclusion that M. Pring had 
been led astray, and considering the different opinions held by 
many persons about the markings of diatoms, one opinion so. 
opposite to the other, it is very troublesome to come to a definite 
conclusion on the subject. 
M. Pring remarks, “as to the small points or circles, figured on 
Fig. 34. 
the surface of the pretended elevations by certain authors. They 
are due to the effects of diffraction, and disappear when an open 
areola is examined.” Now, if we examine a valve of 771. Regina 
or excavata, by direct light through the valve, focussing sharply to 
the flat surface of the valve, we get to the edge of the basé of the 
areole, and viewing the areola, find that the colour is different to- 
that of the field (outside the edge of the valve), proving that we 
are looking through the substance of the areolz ; and if the valve 
has its exterior towards the observer, we have to withdraw the 
objectives by the fine adjustment to reach the apex of the areola ; 
and if the interior is towards us, we lower the objective by the 
same means to reach the bottom of the pit, or concavity of the 
areola. 
The same observations apply to the valves of Stéctodiscus, Tricera- 
tium, and others. 
If these diatoms are viewed by reflected light + on a black back- 
* Fig. 26. Specimen in my cabinet. 
+ See also J. Deby. Bull. Soc. Belg. Mic. vii., 1881, pp. 79 to 82. 
