431 



only in the family Agrionidae (Fig. 45, insu), in which it extends 

 from a point between the mesocoxae and metacoxae, caudo-dorsad to 

 the caudal margin of the first pair of wings. 



Mesepisterna (Figs. 43, 45). — The mesopleural suture, dividing 

 the mesopleura into episterna and epimera, may be traced by locating 

 the lateral articulation of the mesocoxae (Fig. 40, mcp) and the 

 mesopleural wing-process (wp) — a heavily chitinized process extend- 

 ing from the caudo-dorsal margin of the thorax into the membrane 

 at the base of the first pair of wings. The suture will be found to ex- 

 tend cephalad, beginning at the wing-process, parallel to the dorsal 

 carina, as far as the cephalic third of the mesothorax, where it appar- 

 ently forks, and sends one branch cephalad and the other ventrad to 

 the coxal process (mcp). The horizontal fork is a secondary suture 

 and separates the small sclerite above the coxae, the infraepisternum 

 (ieps), from the rather large oblong sclerite, the supraepisternum 

 (seps). 



Mcsepimera (Figs. 43, 45). — The mesepimera lie caudo-ventrad 

 of the mesopleural sutures. In the Coenagrionidae they are fused 

 with the metepisterna and the interpleural suture is obsolete except 

 near the wing bases. In the Agrionidae the interpleural suture is dis- 

 tinct throughout its course, and the metepimera are then elongate 

 sclerites with the dorso-cephalic angles considerably rounded. 



Mctapleura. — The key to the metapleura is the metapleural suture, 

 which may be traced in a similar manner to the mesopleural suture. 

 This may be done by finding the metacoxal articulation and the meta- 

 pleural wing-process (wp), situated at the base of the second pair of 

 wings, and following the suture between the two points. 



Metepisterna (Figs. 43, 45). — The metepisterna are those portions 

 of the metapleura cephalad and dorsad of the metapleural suture (Fig. 

 45, mtsu). Like the mesepisterna they are divided into two separate 

 sclerites, a small one dorsad of and adjacent to the coxae, the metin- 

 fraepisternum, and a larger, elongate one dorsad of the metinfraepi- 

 sternum and extending from the cephalic margin of the latter caudo- 

 dorsad to the bases of the wings — the metasupraepisternum (seps). 

 The latter is narrowed to about half its width above the infraepisternum 

 and usually bears the metathoracic spiracles (Fig. 43, mtsl) within 

 the constricted portion. In many species there is a secondary suture 

 extending between the spiracle and the metapleural suture (Fig. 45). 



Metepimera (Figs. 43, 45). — Caudo-ventrad of the metapleural 

 suture is the metepimeron. The metepimera are contiguous on the 

 ventro-meson. In the Agrionidae the boundaries of the sclerite, be- 

 ginning with the metacoxal process (mtcp), may be indicated as fol- 



