I4 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 134 
The anepisternum (aet.) is a large sclerite which is bounded an- 
teriorly by the spiracular peritreme, anterodorsally by a small mem- 
branous area which bears the metanotal prescutum, and posterodor- 
sally by the base of the fore wing. This dorsal extension is typical of 
odonate naiads. 
The katepisternum (ket,) extends ventrally in front of the coxal 
cavity and meets the basisternum on the anterior margin of the meso- 
sternal surface. The katepisternum is bounded anteriorly by a flexible, 
vertically folded, partially sclerotized area beyond which lies the 
prothoracic epimeron, 
The epimeron (emz) has become fused with the posteriorly adja- 
cent metathoracic anepisternum. This fusion has resulted in the 
suppression of the mesopleural-metapleural intersegmental suture 
but the posterior portion is obviously the metanepisternum since it 
bears the metathoracic spiracle. The resultant large composite sclerite 
is reflected ventrally and passes behind the coxal cavity to the sternal 
surface, where it is produced into a large forwardly directed lobe 
which bears numerous long curved spines and setae. 
The mesothoracic spiracle (spz) lies in the upper part of a long 
sclerotized peritermal plate between the pronotum and the meso- 
thoracic anepisternum. This is the only spiracle that becomes im- 
mediately functional for respiration upon emergence of the naiad 
from the water prior to transformation. The remaining thoracic and 
abdominal spiracles are functional in the adult only (Snodgrass, 
1954). 
METAPLEURON: The metathoracic pleuron is somewhat similar to, 
but smaller than, that of the mesothorax described above. It is divided 
into two portions, the episternum and the epimeron, by the pleural 
suture (pls3), which proceeds obliquely dorsocephalad from the coral 
process (cxps) to the center of the pleuron and then swings posteri- 
orly to the wing base. The episternum is further divided by a distinct 
arcuate suture into an anepisternum and a katepisternum. 
The anepisternum (aets), which bears the metathoracic spiracle 
(sps), is fused with the mesothoracic epimeron, i.e., it is not anteri- 
orly delimited by an intersegmental suture. It extends dorsally to the 
base of the hind wing. ; 
The katepisternum (kets) or lower region of the episternum is 
smaller than the anepisternum. In addition to its normal pleural posi- 
tion, the katepisternum narrows abruptly to pass in front of the coxal 
cavity and is reflected ventrally where it expands and extends to the 
basisternum. This sternal portion is fused with the posteriorly adja- 
cent, ventrally isolated katepimeron, from which it is partially de- 
