NO. II NAIADS OF DRAGONFLY GENUS PLATHEMIS—LEVINE I9 
well developed. All three segments of the tarsus bear on their ventral 
surfaces several heavy spurs which decrease in size distally. 
The PRETARSUS (fig. 19) or terminal region of the leg consists of 
claws, empodium, and unguitractor. The claws or ungues (un) are 
the largest parts of the pretarsus, and they articulate with a small 
dorsal process of the distitarsus. Ventrally, the bases of the claws are 
connected with membrane which is also closely attached to the mesally 
located unguitractor (ut). The unguitractor is a sclerite that can be 
retracted into the distitarsus by the action of muscles in the tibia 
which are attached to the unguitractoral tendon which is in turn at- 
tached to the unguitractor. The unguitractor is partially hidden by 
the plantella. An empodium (emp) is attached to the distal end of 
the unguitractor by a narrow stalk. The remainder of the empodium 
is more or less paddle-shaped. 
ABDOMEN 
The abdomen of Plathemis lydia (figs. 20-24) is elongate and 
slightly longer than the head and thorax combined. It is broadest at 
the fifth segment and tapers gradually posteriorly to the tips of three 
horny processes enclosing the anus. The abdomen consists of ten 
complete annular segments and probably rudiments of the eleventh 
and twelfth segments (Heymons, 1904). 
ABDOMINAL TERGA 
The abdominal terga (figs. 20, 24) are distinctly transversely 
elongate in shape. They increase slightly in the transverse dimension 
from the first to the fifth segment and then shorten to give a markedly 
tapered appearance to the abdomen. The middorsal line and lateral 
margins are produced in the form of keels, giving the abdomen a 
triquetral appearance. Sharp, posteriorly curved dorsal hooks (dh) 
are present on the dorsal midline of segments three to six, but absent 
on the remaining segments. The dorsal hook on segment five is the 
longest of the four hooks, all of which are densely covered with sharp, 
spiniform setae. Long, sharp lateral spines (Isp) are present on the 
posterolateral angles of segments eight and nine, one pair per seg- 
ment. The spines are approximately one-sixth as long as the segments 
bearing them. Smaller spines are present in rows on the lateral and 
posterior tergal margins and scattered generally over the dorsal sur- 
face. The spines gradually increase in size and density as they pro- 
gress posteriorly. The terga are also adorned with a few scattered 
setae and long lateral hairs. 
