14 
Psyche 
[March 
Unique and apparently primitive characters. — The prosternum of 
these wasps is of unusual interest. A large, flat, triangular or diamond- 
shaped prosternum occurs in a few sawflies (e.g. Syntexis) and a few 
parasitoids (e.g. Spilochalcis) , but virtually all Aculeata have the 
prosternum much reduced and somewhat sunken, or even practically 
absent. The Sapygidae have a somewhat larger and less sunken 
prosternum than most Aculeata, but even here the resemblance to the 
Scolebythidae is not great. The free proepimeron is also most unusual. 
I find no evidence of this structure in most Aculeata examined, but in 
the Plumariidae the proepimeron is fairly well developed, although 
not quite so completely set off as in the Scolebythidae. The large first 
sternite of the abdomen, which extends arcuately backward and broad- 
ly overlaps the second sternite, is also unusual, as in most primitive 
Aculeata the first sternite is short and there is at least some evidence 
of the beginnings of a constriction at this point: this is true in such 
groups as the Anthoboscinae, the Sapygidae, and the Bethylidae. How- 
ever, in the Plumariidae the condition is almost exactly the same as in 
the Scolebythidae. 
Unique and apparently specialized characters. — Here I would 
include the broad mouth opening and powerful mandibles, the reduced 
clypeus, and the strong malar space; on the thorax the elongate proe- 
pisterna, perhaps the large prosternum, and the flattened coxae. These 
characters together surely make up a single adaptive complex, and 
give the anterior part of these insects a striking resemblance to that 
of certain parasitoids which attack wood borers (most particularly the 
Aulacidae). I feel there can be little question that the Scolebythidae 
attack wood-boring larvae, probably of beetles (since most Scolioidae 
and many Bethylidae attack beetle larvae). Probably they enter the 
burrows of the beetles to find their hosts. After I had come to these 
conclusions I sent specimens to Dr. J. G. Betrem for examination, and 
he expressed exactly the same opinion. 
Summary of characteristics. — Of the 25 characters numbered in 
my diagnosis of the family on an earlier page, the following are primi- 
tive aculeate characters not necessarily relating these wasps to any 
other aculeate group: 3, 13, 14, 17, 18, 22. The following characters 
appear especially primitive and unlike other Aculeata: 10, n, 15, 24 
(but the Plumariidae possess 15 and 24, and 10 in some measure). 
The following are bethylid characters: 7, 19, 21 (but see discussion 
above). The following specializations make up an adaptive complex 
appearing to fit these wasps as parasites of wood-boring beetle larvae : 
2, 4, 8, 9, 12, perhaps also 11. The remaining characters are shared 
