My A. si/lvestris has 14 ( S ) and 12 ( 9 ) joints. Another North 
American species, parasitical in the gall of Rliodites radicum 0. S. is, 
in this respect, like the preceding. 
The striking difference in the structure of the abdomen of the % and 
the 9 is, as Mr. Rheinhard informs me, a peculiarity of this genus. 
As to the position of Aulax in the system, that assigned to it by Hartig 
is somewhat doubtful, as, according to his statement, some of its spe¬ 
cies are true gall-producers (^Psenides), others parasites {Inquilinae). 
The further observations of Giraud have not dispelled these doubts. 
Of the European 16 species at present described, seven are said to pro¬ 
duce galls on Salvia, Scorzonera, Papaver rhoeas, Hieracium and 
Gleclioma; three have been reared from galls of other species, (two 
from Rhodites-gAl^ on the rose, one from an oak-gall of Andricus'). 
The N. American Aulax known to me at present, are all parasites. 
A. sylvestris, described below, lives in the gall of Diastrophus; Aidax 
semipicea Harris is obtained from the root-gall of the rose (^Rhodites 
radicum 0. S.), and Avas mistaken by Hr. Harris for the originator of 
this gall. A third species, A. futilis, which I described in my paper 
on the Cynipidae of the oak (Proc. Ent. Soc. Phil. 1, p. 64) is some¬ 
what doubtful, as I was not well acquainted with the characters of the 
genus Aulax at that time, and have accidentally broken since the only 
specimen, which I reared from the gall of Cynips q. futilis 0. S. I 
moreover possess th^e^ther species, all reared from rose-galls, and of 
one of which (A. iH/uscatus 0. S.) I give a short description below. 
This inconstancy in the habits of the species of the same genus is 
rather anomalous, and requires further observation. I would remind 
here of a very common reniform gall occurring on Vaccinium in this 
country, and from which, although collected quite abundantly, I never 
reared anything but two Chalcidii: a Decatoma and a Pteromaloid 
insect. Would this be considered as a sufficient proof that either of 
these insects is the originator of the gall ? The neuration of the wings 
of the species of Aidax, especially the form of the radial area, undoubt¬ 
edly establishes their relationship to the parasitical Cynipidae {Inqui- 
linae'). 
Hartig says (1. c. Ill, p. 334) that the radial area in Aulax is closed 
in some species, open in others. Judging by the structure of this area 
in A. sylvestris and A. semipicea, I am inclined to believe that this 
character, at least in this genus, is a very indefinite one, as the closing 
