420 



areas, two of which, the cephalo-dorsal and cephalo-ventral (Fig. 25, 

 seps, ieps), comprise the episterna, and the caudo-ventral, the epimera 

 (Fig. 25, epm). The ventral areas of the episterna (ieps) are known 

 to odonatologists as the infraepisterna, and the dorsal ones incorrectly 

 as the episterna. For convenience in designating the parts the latter 

 may be known as the supraepisterna (seps). 



Mesostemum. — The mesosternum, that area between the meso- 

 coxae, the caudal margins of the prosternum, and the cephalic margins 

 of the metasternum, is not divided into separate areas, but the furcae 

 are present and the deep f ureal invaginations are very distinct (Fig. 

 24, fi). 



Metaplenra. — The boundaries of each metapleuron are the inter- 

 pleural suture, the metacoxae, the metathoracic wing-cases, and the 

 pleura and sternum of the first abdominal segment. The sclerites are 

 each divided into three parts, the cephalic two comprising the 

 metepisternum (supraepisternum and infraepisternum), and the caudal 

 one, the metepimeron. The metathoracic spiracles are located on these 

 pieces near the union of the dorsal border of the metinfraepisternum 

 with the interpleural suture. 



Metasternum. — The metasternum (Fig. 24, mtst) is similar in 

 shape to the mesosterntim, but is divided by sutures into three areas. 

 The invaginations of the metafurcae are also prominent and a suture 

 extends caudo-mesad from each. The two sutures unite on the meson, 

 extend caudad for a short distance, separate again, and extend laterad 

 and caudad of the coxae. The areas on each side of the mesal line are 

 the two halves of the sternellum (mtsm). Caudad of the sternellum 

 is a broad sclerite possibly representing the first abdominal segment. 

 This may be known as the intersternum (Fig. 24, ints). There is no 

 corresponding sclerite on the dorsum caudad of the thorax, but it may 

 be that the latter portion has been lost. If, however, the intersternum 

 be considered as a vestige of an abdominal segment, it will be found 

 by actual count that there are twelve segments represented in the abdo- 

 men of the nymph, a fact which makes one skeptical of the above inter- 

 pretation. In some species, the area is membranous, and it is possible 

 that the sclerite is nothing more than accessory membrane which has 

 subsequently become chitinized. 



Trochantins. — The trochantins are wanting in the Zygoptera, and 

 the mesal part of the coxae articulates directly with the sterna. 



Legs. — The legs are usually slender and not well adapted for cap- 

 turing prey, the labium being wholly relied upon for that purpose. 

 The coxae are nearly spherical and slightly compressed. The trochan- 

 ter consists of two segments. The proximal segment is narrow and 



