Norman, on Diatomacea. 
9 
Hab. — Stomach of Asciclians, Shark Bay, western coast 
of Australia ; kindly communicated by Dr. Macdonald. 
This singularly beautiful form is exceedingly rare in the 
above-mentioned gathering. It belongs unquestionably to 
the group of forms of which Nav. lyra is the type. The re- 
markable row of bosses on the smooth bands renders it 
distinct from any known species. 
It may be remarked that, in describing the structure of 
Coscinodiscus fuscus and Aulacodiscus Sollittianus, I have 
designated the markings on the valves " granules/^ instead 
of adopting the usual method of calling them areolae, or cells. 
Hitherto, I believe, most authors have adopted the latter desig- 
nation in describing the various species of Coscinodiscus, 
Aulacodiscus, Eupodiscus, &c., and have, by so doing, in my 
opinion, overlooked the real nature of the construction. 
Dr. Wallich has done good service in pointing out the true 
structure of the markings oi Pleurosigma, and I feel con- 
vinced that all the above-mentioned discs are constructed on 
the same plan, differing only in the form of the elevations or 
granules, and their arrangement on the surface of the valve. 
In Pleurosigma the markings are four-sided elevations; 
while in Coscinodiscus, Eupodiscus, &c., they are circular 
when not crowded, but assuming the irregular or hexagonal 
form when pressing on each other. The same structure ap- 
pears to exist in Biddulphia, Isthmia, &c., and probably in 
all diatoms, not even excepting Triceratium favus, the raised 
portions of silex only differing in form. 
On examining a valve of Coscinodiscus gigas, or lineatus, 
for instance, with a good one fourth or one twelfth, we find 
the colour of the valve, in the interstices between the granules, 
to be pink, whereas the granules themselves are white, or 
colourless. 
The true structure, however, is better seen in valves 
where the granules are more circular, and not so much 
crowded together. Here the structure will be apparent at a 
glance. 
