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AQUARIUM MOLLUSCS. 
jOR some time I have been experimenting with Fresh- 
I water Molluscs with a view of discovering the most 
I useful species for the aquarium. 
It is generally believed that most kinds of the Gas- 
tropoda are suitable, more or less, but this has not been my expe- 
rience. I would exclude the whole of the genus Limiaa, as in 
addition to their predacious habits, so far as the plants of the 
aquaria are concerned, the result of their dirty habits are apt to 
set up disease when least expected. 
The genus Planorhis I place in an intermediate rank as 
purifiers of the water, from my point of view. They most cer- 
tainly eat confervoid growths in preference to the ordinary 
plants, but seldom touch actual decaying vegetable matter when 
they can find conferva. 
I have come to the conclusion that Palndina vivipara is by far 
more to be depended upon than any other Gastropod. They 
prefer decaying vegetable matter to any other food, which they 
are continually clearing away. They have also a very handsome 
shell, are very hardy, and not so apt to die and foul the water of 
the tank, as are some of the other species. Apart from their use 
as scavengers of the tank, they are particularly interesting in 
other respects to the enquiring naturalist. As their specific 
name implies, they bring forth their young alive, and there is 
sure to grow up a little colony of young Paludina wherever the 
species is introduced. They come into the world very perfectly 
formed in comparison with those molluscs which are hatched 
from ordinary spawn. They are very pretty little creatures, and 
look very ornamental as they crawl upon the plants and rock- 
work of the Aquarium. 
The interesting mollusc, Bithynia ientaculata may also be 
safely introduced, as also its ally, Valvata piscinalis. I have 
found that these two species prefer to feed on the conferva 
which grows on the glass side of the tank, rather than on 
decaying matter. 
A useful bivalve, and also one that is easily obtained, is 
Anodon cygnca. Acting as a living filter, a healthy specimen or 
two will keep the water as clear as a spring. 
Drcissensia polymorpha — that mollusc which was found in such 
profusion in the old London water-pipes — is also useful and 
interesting. It is always the safest method to place any molluscs 
intended for the aquarium in quarantine for about a week, for 
as they are generally found amongst decaying matter in their 
natural habitat, they are very apt to introduce deleterious sub- 
stances into the tank, if transferred immediately without going 
through the cleansing process. This remark applies to all 
molluscs, whether univalve or bivalve. 
C. M. Hall. 
