the thinnest glass. They possess a pair of large membranous fins, which closely resemble the wings of a butterfly, and by using these organs in a flapping manner, the little animals swim briskly about.
Perhaps some of my readers will expect me to include the beautiful Paper Nautilus (Argonauta), among swimming Mollusks; seeing that the poets have claimed for it the honour of teaching navigation to man:—
"Learn of the little Nautilus to sail,
Montgomery, the poet of the ocean, thus beautifully expresses the popular notions concerning it:—