160 PHILIP P. CALVERT. 



In the members of that subfamily, in front of the metastigma, a 

 suture is to be seen a short distance behind the humeral suture, 

 starting, likewise, from beneath the base of the front wing, and 

 meeting the humeral suture behind the second coxa. This suture 

 is the fird lateral suture of Rambur, and the space between it and 

 the humeral suture is the mesepimeron. Following and parallel to 

 the first lateral suture in the Calopteryginte is the second lateral 

 suture, from beneath the base of the hind wing to the rear of the 

 third coxa. From near its lower extremity a short curved suture 

 passes to the front of the third coxse, so that a metinfraepisiernum is 

 formed, corresponding in position to that of the mesothorax. The 

 space between the first and second lateral sutures is the metepistermim. 

 Behind the second lateral suture the metepimeron extends ventral- 

 wards to the sternuni, with which it is apparently fused in front, but 

 from which it is separated for the most part by the longitudinal 

 latero-ventral metathoracic carina. 



The mid-dorsal thoracic carina and the first lateral suture thus 

 correspond, and so also the humeral and second lateral sutures. 



In some Calopteryginte (e. g. Rhinocypha), and in the other sub- 

 families, the greater part of the first lateral suture is obliterated, 

 onlv the lower part up to about the level of the metastigma, and 

 sometimes the upper extremity (e. g. Lestes), remaining. Thus 

 mesepimeron and metepisternum form a single piece. 



The interpretation of the thoracic pleura here given, which is essentially that 

 of Packard (1), as against those of Brauer and Walsh, seems justified by the 

 metameric arrangement of the wing muscles. Brauer {I. c.) holds that what are 

 above regarded as the mesepisterna are really the prescutum of the mesothorax. 

 An examination of the wing muscles (see the description, pos<, and PI. II, figs. 

 12, 13), will show that both as regards its relation to the other pleural sclerites, 

 and to the position and origin of the muscles of the front wiug, the mesepister- 

 num is the homologue of what is above termed the metepisternum.® Walsh, 

 however (Proc. Ent. Soc. Phila., II, pp. 269, 270), regarded the division between 

 meso- and metathorax as marked by the second lateral suture, while the first 

 lateral suture he termed " false," or " supernumerary." To this it may be replied 

 that the position of the first lateral suture corresponds to the line of separation 

 between the muscles of front and hind wings, the arrangement of which mus- 

 cles is so clearly metameric (fig. 12, being that of an Aeschna, cannot show the 

 first lateral suture as it is obliterated). 



The mesosternum is relatively small, and lies between and in front 

 of the second coxse. The metasternum is probably all that area 



* Compare also the development of the mesepisterna, post. 



