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Trochi, are found attached to rocks on all our coasts; of the Ear shells (Halotis), and Boat shells (Chiton), we shall have much to say hereafter when we meet with them.
Of the Pulmonifera or air-breathing Mollusca, some are terrestrial, others fresh-water, and many inhabit damp places near the sea; their respiratory organ is so simple a form of lung, that this order is called by Gray, "concealed lunged," as the orifice is small and valve—like to guard against the entry of water in the aquatic tribes, and to prevent the rapid desiccation in the land snails.
The latter do not abound in Australia, but we find abundant interest in the beautiful shells which exist in the Yarra, the Moorabool, the Merri, and other of our rivers, lurking on the large, ovate, floating leaves of the Nymphæa-like Damasonium, or the broad paler Potamogiton (Pond-weed), which is always so gay and refreshing an object, but these we must needs put into an Aquarium to watch with the aid of a pocket lens their structure and habits. We place along with them some of the green scum which covers the surface of the water (we say scum, but it is in reality a beautiful freshwater Alga,) a Zygnema in conjugation, and a few plants, such as Chara, the velvety Azolla rubra or pinnata, one or the other of which is to be met with on the Merri, at Warrnambool; the Moorabool, at Geelong; on the lagoon in the Botanical Gardens, Melbourne, and such like situations. The flat many-whorled shell, so brittle,—is a Planorbis, this other, ovate-shaped and also very thin with a large aperture, is a Physa, so called from its resemblance to a pouch;
