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{EtdameUibrunchiii), or whether the gills have lost their function 
of respiratory organs (Septihranchia}. Unfortunately it would 
be difficult to demonstrate these anatomical features sattsfact- 
urily even with a series of w^t preparations, at least in a 
public Museum, and the visitor will have to accept these four 
orders on good faith. The collection has no specimens belong- 
ing to the first and the last of these orders, but the second and 
the third are well represented. 
Filibranchia. We begin with a very unusual looking 
shell, Placuna placenta. It is of medium size, 4 to 5 inches 
in diameter, flat and almost circular, thin and so transparent 
I hat according to Tenison Woods it is used instead of glass in 
window frames in the Philippines, Macao etc. Ptacuna sella 
is much larger, about 8 inches in diameter, al5t> nearly circular, 
but twisted somewhat in the shape of a saddle from which it 
has received its popular name of 'Saddle-Oyster/ Both of 
them are asymmetrical, Tht next sub-order includes symmet- 
rical animals, like the Arc Shell {Area granosa). A collection 
of them, from the Fish Market, presented by Mr. C H. Clarke, 
is exhibited. The valves are boat shaped, ribbed and can 
always be told by their straight hinge which bears numerous 
teeth. It is edible.— The well-known Mussel {Myiilus) and its 
allies form a third suborder. Exhibited is M. smaragdmtts, 
from Singapore, with a bright grass green shell The most 
important suborder of the Filihraiichia is that of the Pecthiacea, 
It contains first of all shells with strange wing-like processes, 
as Avicula macraptera. Specimens of it, from Pulo Branit 
were presented by Lieut. C B. Harvey in 1897. Of the greatest 
economic importance is the Pearl Oyster {Meleagrina margarit^ 
fern). Some specimens of it, and apparently the first ones from 
this neighbourhood, were obtained two years ago close to Singa- 
pore in three fathoms of water by Mr. W. F, C. Asimont, The 
shells were exhibited at the Agricultural Show in August, igo^ 
and were subsquently presented by Mr, Asimont to the 
Museum. Richest in Pearl Oysters is the North Coa^t of 
Australia, and the shells of this particular species are of value 
not only through any pearls they may contain, but also 
because their mother-of-pearl may be turned into the most 
varied useful articles. The shells of the Ceylon Pearl^yster 
(Meleagrina fucatal are too small and too thin to be of much 
use and are of value only through their pearls. The peaHs 
are pathological products, being a secretion of the mantle 
around foreign bodies. In the Pearl Oyster of Ceylon the 
foreign body is stated to be a small parasite, the scolex (t)r 
