no. II NAIADS OF DRAGONFLY GENUS PLATHEMIS—LEVINE 9 
surface is mostly unsclerotized. It bears a curious group of eighteen 
short spines arranged in a semicircle just ventrad of the transverse bar 
of the hypopharyngeal suspensorium as well as numerous other setae 
and spinulae scattered over the surface. The lateral, distal, and aboral 
surfaces are sclerotized. The former two bear many long, curved 
setae and spines, while the latter is glabrous. 
The hypopharyngeal apodeme (hap) is a characteristic feature of 
the dragonfly naiad. Its shaft extends posteriorly through the head 
below the tentorium and the crossbar is embedded in the posterior 
edge of the base of the postmentum of the labium where it is held in 
place by “small apical brushes of fine fibers” (Snodgrass, 1954). 
The suspensorium of the hypopharynx consists of a transverse bow- 
shaped bar (ths) on the dorsal margin of the base of the hypopharynx 
and two pairs of arms, oral (ohs) and lateral (ths), which are con- 
tinuous with the former. 
The nymphal Lapium consists of two major parts hinged on 
each other by an elbowlike joint. Numerous inconsistencies in the 
terminology of these parts are present in the literature. The present 
writer has followed the labial nomenclature of Corbet (1953) and 
Snodgrass (1954) in calling the proximal part the postmentum and 
the distal portions the prementum and its distal lobes the labial palpi 
and the ligula. In the retracted position the labium is folded so that 
the aboral surface of the postmentum is pressed against the ventral 
surface of the head and thorax, and the distal adoral surface, formed 
by the prementum, the palpi, and the ligula, forms a deep spoonlike 
mask that covers the face and other mouthparts up to the antennal 
bases. In protraction, the prementum is thrust out beyond the head 
by a forward swing of the postmentum. At the same time the disto- 
lateral lobes are thrown wide apart with their movable hooks erect 
(Amans, 1881—from Snodgrass, 1954). 
The labial palpi (lbp) are curved lamellar structures forming part 
of the spoonlike mask. In broadest perspective, as in figure 13, each 
palpus appears more or less triangular in outline because of its greatly 
expanded distal portion. Each palpus possesses a prominent movable 
hook (mh) on its distolateral angle and 10 long, slender lateral palpal 
setae (Ips) lying nearly parallel to its outer margin. In addition, the 
distal margin of the palpus bears seven or eight teeth (dpt), which are 
mesally directed and about as broad as long. Each tooth is provided 
with one to three short, spiniform setae (dps). The mesal margin of 
each palpus also bears several minute setae (mps). 
The ligula (lig) lies between the bases of the palpi and is fused 
with the prementum. The median portion of its distal margin is an- 
