1951] 
Broivn and Cheng — Psilobethylus 
143 
records for the wasps are all indicative of a habitat in 
the upper soil layers or at the level of the soil cover. 
Among the relatively meager material at our disposal 
can be recognized what seem to be two distinct species, 
separable on the basis of size, proportion, sculpture and 
shape of head. The smaller and smoother of the two species, 
lucidus n. sp., is set up for specimens stemming from Il- 
linois, West Texas, North Carolina and Tabasco in south- 
ern Mexico. In view of slight differences between indi- 
viduals from these widely separated localities, it seems 
probable that lucidus contains more than one specific entity. 
The differences are so elusive, however, and the variation 
within series relatively so great that we cannot confidently 
assort them taxonomically without the corresponding males. 
It must be borne in mind that each of the locality-series 
probably represents the offspring of a single female. Such 
a situation creates constancy within series and differences 
between series that are often illusory in the systematic 
sense, since not only may the mothers show slight in- 
dividual, non-taxonomic differences, but the hosts and the 
differing food supplies they afford may alter radically the 
structure of individuals from one brood to another. In 
fact, even the large, densely sculptured foveolatus may 
eventually prove to be nothing more than a form of lucidus 
arising through differential feeding. The differences in 
size, shape, and especially in sculpture are of such magni- 
tude that we feel fairly confident in separating the two as 
species at the present time. 
Psilobethylus foveolatus n. sp. 
(Plate 13, figure 1) 
Holotype female: Total (synthetic aggregate) length 
2.20±.04 mm.; head length, maximum measurable, 0.53 
±.005 mm.; alitrunk length, maximum diagonal measure- 
ment in lateral view, 0.72±.01 mm.; cephalic index (maxi- 
mum head width expressed as a percentage of head length) 
75 ±1. Habitus as in figure, except that (in both figures 1 
and 2) the insertions of the antennae are depicted more 
boldly and more strongly set off than they are in the actual 
