a piece of money amongst the Romans, being the tenth part of the denarius, and equal in value to the as. It was called libella, as being a little pound, because equal to a pound of brass.—Its value in our money is 1 ob. 1 qu. or a half-penny farthing. See Money.

Libellula, in zoology, a genus of four-winged flies, called in English dragon flies, or adder flies; the characters of which are these: The mouth is furnished with jaws: the feelers are shorter than the breast; and the tail of the male terminates in a kind of hooked forceps. There are 21 species, chiefly distinguished by their colour. They have all two very large and reticulated eyes, covering the whole surface of the head. They fly very swiftly; and prey upon the wing, clearing the air of innumerable... able little flies. They are found in August and September in our fields and gardens, especially near places where there are waters, as they have their origin from worms living in that element. The great ones usually live all their time about waters; but the smaller are common among hedges, and the smallest of all frequent gardens. The smaller kind often settle upon bushes, or upon the ground; but the large ones are almost always upon the wing, so that it is very difficult to take them. Their eyes are beautiful objects for the microscope. The largest species is produced from a water-worm that has six feet, which, yet young and very small, is transformed into a chrysalis, that has its dwelling in the water. People have thought they discovered them to have gills like fishes. It wears a mask as perfectly formed as those that are worn at a masquerade; and this mask, fastened to the insect's neck, and which it moves at will, serves it to hold its prey while it devours it. The period of transformation being come, the chrysalis makes to the water-side, undertakes a voyage in search of a convenient place; fixes on a plant, or sticks fast to a bit of dry wood. Its skin, grown parched, splits at the upper part of the thorax. The winged insect issues forth gradually, throws off its flough, expands its wings, flutters, and then flies off with gracefulness and ease.

The elegance of its slender shape, the richness of its colours, the delicacy and resplendent texture of its wings, afford infinite delight to the beholder. The sexual parts of the libellulae are differently situated in the male and female. It is under the body at the joining of the thorax, that those parts are discovered in the males: those of the females are known by a slit placed at the extremity of the body. Their amours conclude in a rape. The male, while hovering about, watches, and then seizes the female by the head with the pincers with which the extremity of his tail is armed. The ravisher travels thus through the air, till the female yielding to superior strength, or rather to inclination, forms her body into a circle that terminates at the genitals of the male, in order to accomplish the purpose of nature. These kind of rapes are common. Libellulae are seen thus coupled in the air, exhibiting the form of a ring. The female deposits her eggs in the water, from whence spring water-worms, which afterwards undergo the same transformations.