22 
mentioned. In the Cordulegasteride and Libellulide the labium 
is spoon-shaped, covering the face, the lobes broad and sub- 
triangular, fitting closely against the median lobe and to each 
other. The teeth of the opposed terminal margins are, in the 
former family, large, acute, and interlocking, but in the latter 
they are rounded crenations, at most not higher than broad. 
These are tipped with short hairs, however, which when wet 
make them appear pointed. On the inner surface of each lat- 
eral lobe may be a row of several conspicuous sete, the lateral 
sete, and a similar row on each side of the middle of the median 
lobe— the mental sete. The antenne are usually small and 
cylindrical, 6- or 7-jointed, but are broad and flattened in the 
Petaluride and Gomphide,and only 4-jointed in the latter family. 
The thorax and its appendages are not extensively used in 
the classification of the nymph. On each side of the prothorax, 
in the Aschnide, are a pair of small tubercles, the supracoxal 
processes, best viewed in profile from above. They are fairly 
constant in form for each species. The tarsal joints are usually 
three in number, but in the Gomphide there are only two joints 
in the anterior and middle tarsi. The suture between the first 
two tarsal joints is oblique, making the basal joint much 
shorter above than below. The comparative length of these 
two joints, measured on the dorsal line, is a useful distinction in 
the Libellulide. As the suture between them is usually marked 
in darker color above, it is easily located. The wing-pads vary 
in size with the age of the nymph, being at first entirely want- 
ing. In the adult nymph four or five abdominal segments usu- 
ally remain exposed behind them. 
The two main groups of dragon-flies are quite unlike in the 
terminal appendages of the nymphal abdomen. In Zygoptera 
it ends in three large leaf-like gills, while in the Anisoptera the 
last segment—the tenth abdominal—bears five small tapering 
appendages, which converge and form a valve closing the rectal 
opening. The middle one above is the superior appendage, the 
lower pair are the inferior appendages, and on each side of the 
superior appendage, above the inferiors, are the lateral append- 
