1951] 
Carpenter — Oliarces 
39 
of posteriorly, could easily be modifications of those of 
Rhone. 
The terminal abdominal segments of the female of Rhone 
are shown in text-figure 3A. Tillyard, in describing these 
(1919, p. 426), states that the eighth, ninth and tenth ab- 
dominal segments “are more or less fused together, form- 
ing the projecting end of the abdomen.” In alcoholic speci- 
mens, however, the segments are perfectly distinct. The 
eighth tergite extends further ventrally than the seventh; 
and the ninth, as in nearly all Planipennia, reaches all the 
way to the ventral surface. The eighth sternite is not visible 
externally. The ninth sternite in all the ithonids is posterior 
to the ninth tergite and is enlarged to form the sand-plow or 
psammarotrum. Its two lateral plates are fused dorsally 
by membranes but are, of course, separated posteriorly in 
the region of the gonopore. The psammarotrum bears a 
pair of conspicuous processes, directed ventrally ; these were 
thought by Tillyard to be used as tactile organs during ovi- 
position. The tenth tergite is short, hood-shaped and bears 
the trichobothria. In Oliarces (Figure 3B) the ninth tergite 
is not so long ventrally as in Rhone and the ninth sternite 
is reduced to a pair of very small plates, scarcely extending 
beyond the tenth tergite. That these plates do comprise the 
ninth sternite is indicated by the presence of a pair of small 
distal papillae, which, although they project dorsally, are 
clearly homologues of the longer, ventral processes in Rhone. 
No true psammarotrum, comparable to that of Rhone , is 
formed, but the structure is there in reduced form. The 
tenth tergite of Oliarces is similar to that of Rhone, except 
for a slight difference in its shape. 
From the evidence reviewed above, Oliarces appears to be 
closer to the Australian ithonids than to any other Neu- 
roptera. This resemblance is, in fact, so close that only one 
modification need be made of Tillyard’s definition of the 
family ; this is the recognition that the psammarotrum may 
be very small or vestigial. 3 It is noteworthy in this con- 
3 Tillyard also stated in his definition of the Ithonidae that the fore 
wings were of tougher consistency than the hind, being somewhat 
leathery; but this is certainly not true of Heterithone pallida, which 
Tillyard himself described as having very transparent and colorless 
wings. 
