432 



lows: — The margin extends ventro-mesad (Fig. 40), meeting its fel- 

 low from the opposite side on the meson, then extends caudad half- 

 way from the coxae to the first abdominal segment, bends laterad to 

 the elevated lateral carina, caudad again to the abdomen, then dorsad 

 (Fig. 45) along the wing bases to the metapleural suture (mtsu), 

 which forms the dorso-cephalic border of the sclerite. At the caudo- 

 ventral angles of the epimera there is a small triangular sclerite which 

 if apparently cut off from the main portion of the epimeron. The 

 primary suture follows the ventral margin of the deep fold which 

 occurs at this point. The latero-ventral carina does not follow the 

 ventral suture of the epimera all the way from the abdomen to the 

 coxae, but, instead, follows a more direct line along the ventro-lateral 

 margins of the thorax and diverges from the suture half-way from 

 the abdomen to the coxae (Fig. 40). In the Coenagrionidae the 

 sutures marking the ventral borders of the epimera are less distinct 

 and do not follow quite the same course (Fig. 42). 



Mesostcniinii and Mctastcrnuin. — The approximation of the coxae 

 in the adults of Zygoptera has brought about profound changes in the 

 mesosterna and metasterna. 



Mcsostcrnmn (Figs. 40. 42; mst). — The key to the mesosternum 

 lies in the invaginations of the furca (mfi) which mark the caudal 

 limits of the sternum. In the Agrionidae the elevated parts of the 

 sternum and sternellum form a distinct hour-glass figure with the furca 

 on either side of the contracted portion. The margins of the sclerites 

 are, however, parallel to the elevated portions, but are somewhat de- 

 pressed. If. the cephalo-lateral angles of the sternum are followed 

 to the sides of the thorax they will be found to extend nearly as far 

 dorsad as the dor.sal margins of the mesinfraepisterna. The cephalo- 

 lateral arms are expanded dorsad, and there are apparently several 

 sclerites represented in the upper portions, possibly the remnants of 

 the mesopresternum (Figs. 43, 45; pst). Along the lateral margins 

 of the sternum cephalad of the furcae there are obscure invaginations 

 which represent the prefurcae (mpf). These are difficult to see from 

 the exterior unless the cuticle is cleared. 



Mcsostcrncllum (Figs. 40, 42 ; mstm). — The mesosternellum is 

 similar in shape to the sternum except that the caudal margin is convex 

 and heavily chitinized in some groups, notably the Agrionidae. The 

 chitinized portions represent furcellae. From the caudal margin of 

 the mesosternellum there extends a short, heavy, chitinous projection 

 which sinks into the metathorax, and is lost from sight beneath the 

 metasternella. This is a part of the metasternum (Figs. 40, 42). 



