The Julia, or Libellula grandis (Linn.), has been separated from the Libellulæ by the great entomologists, such as Fabricius and Latreille, and included in the genus Aeshna (Phœbus, what a name!), preserving the descriptive adjective grandis. What are the reasons put forward to justify this separation? Principally, the form of the abdomen, and the position of those little smooth and simple eyes, like tiny pearls or pearlets, which we call ocelli. In the Libellulæ, properly so called, the ocelli, three in number, are situated on either side and on the exterior margin of a kind of semi-triangular vesicle, and the abdomen is slightly depressed, and not unlike a club; while in the Aeshnæ elongated, and almost cylindrical.
The Aeshna grandis (or the "Julia") is one of the largest of the British species. Its head is large, and its eyes are of a brown colour shading into blue; the yellow thorax has two bright yellow bands or stripes obliquely painted on each side. The abdomen is of a reddish or even rusty brown; generally spotted with white and yellow at the top and bottom of each wing. This species haunts the vicinity of streams and "silent pools."
We come, in due order, to the Aeshna forcipata, or "Carolina," with its dirty yellow head, and its greenish-yellow thorax, the latter marked on each side with three oblique lines of black: the abdomen is black, and composed of segments laterally spotted with yellow.
Fig. 38.—Male and Female of the Agarion virgo.
The Libellula, which the illustrious Geoffroy designates "Louisa," is, according to modern entomologists, neither a Libellula nor a Aeshna, but a species of Agarion,—the Agarion virgo (Libellula virgo, Linn.) The Agarions are distinguishable from the Libellula and the Aeshna by their remarkably thin, filiform, and exceedingly elongated abdomen, and by the three ocelli arranged triangle-wise on the top of the head.
The "Louisa" (AgarionAgarion virgo) is by no means uncommon in England, and may be found along the upper course of the Thames, the Avon, and other rivers. It is easily recognised by its frail slender body, shining with metallic blue reflexes. There are numerous varieties, distinguished by their varieties of "light and shade." The spotless green-winged species is the "Ulrica" of Geoffroy. The two sexes are not alike. In the centre of their delicately-reticulated wings the males have a large bluish-brown spot, which is wanting in the females.
The genera Libellula, Aeshna, and Agarion compose the small family of the Libellulites—a family plainly and conspicuously characterised by the size of their head, and by the two pairs of diaphanous wings of almost equal dimensions (the posterior pair is a little shorter than the anterior), which, while the animal is at rest, are kept horizontally extended.
