16 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 134 
vergent metapleura. The anterior margin of the metasternum is unde- 
marked from the posterior portion of the mesosternum. 
The basisternum (bs;) is a small transversely elongate area in the 
anterior portion of the metasternum situated between the ventrally 
extended portions of the metapleural katepisterna. 
The poststernum (ps3), the largest sternal sclerite, is the posterior- 
most portion of the metasternum. It is roughly triangular in outline, 
with the blunt apex directed forward and the basal angles reflected 
upward on the pleuron behind the coxal cavities. The poststernum 
intervenes between the pleural and ventral portions of the metep- 
imeron. 
The furcal pits (fps) have become isolated and lie in the lateral 
ends of a deep inflection that partially separates the ventrally reflected 
episternal and epimeral plates. 
WINGS 
The wing pads (fig. 15) of a dragonfly naiad are held igverted on 
the back with the spiniferous costal margin uppermost. One distinct 
axillary sclerite is present at the base of the adult wing (Snodgrass, 
1909) but this sclerite is not demarked in the naiad. 
WING TRACHEATION: The veins of the adult wings are preceded 
by tracheae in the nymphal wing pads. “Springing from a basal 
tracheal trunk that lies just inside the thorax, there are six tracheae 
extending out into the wing sac” (Needham, 1951). These tracheae 
are indicated externally on the wing pad surface by rows of well- 
developed setae. The tracheae themselves are best observed in freshly 
killed specimens in which the tracheae are filled with air (Needham, 
1903), but the present writer observed the tracheae through the 
morphologically ventral surface of the left wing pad by rendering 
dried specimens translucent with the addition of either alcohol or 
xylene. 
In describing the position of these tracheae, the Comstock-Needham 
system of wing-venation terminology has been used. 
The fore wing (w.) of Plathemis lydia is rather narrow and 
elongate. Six tracheae extend out into the wing sac: costa, subcosta, 
radius, media, cubitus, and anal. é 
The costa or costal trachea is almost completely atrophied. The 
remaining portion is fused into the thickened leading edge of the wing. 
The subcosta (Sc) is shallowly forked at its terminus, which is 
approximately two-thirds the distance from the wing base to the apex. 
It sends a short branch obliquely forward to the nodal region (nd) 
