34 
[April 
opinion, of little practical value, as anybody can satisfy himself by try¬ 
ing to count them. As for the number of joints of the antennm, it 
seems to vary. One of the species described below (Z). nebulosus) has 
14 ('S ) and 13.( 9 ) joints; Griraud’s D. scahiosse has the same num¬ 
ber; of his D. areolatus he possessed only the 9 and it likewise has 13 
joints. The other N. American species, however,'which I describe 
below (Z>. cuscutaeformis) has, like Hartig’s D. ruhi 15 ( S ) and 14 
( 9 ) joints.* What Hartig says about the antennae of the % (1. c. p. 
410, at bottom), ‘‘ that the last joint is subdivided in two joints of 
nearly equal length, thus making 15 joints”, seems to indicate a struc¬ 
ture similar to that of D. cuscutaefomis % , where the 15th joint ap¬ 
pears to be a mere subdivision of the 14th. 
One of the most curious circumstances connected with the history 
of two North American blackberry galls, observed by me is, that be¬ 
sides the DiastropJius^ apparently the genuine originator of the gall, 
they produce another gall-fly, probably parasitical, belonging to the 
genus Aulax Hartig, and showing the most striking resemblance in 
size, coloring, and sculpture, to the Diastroplms^ their companion. The 
one is the very counterpart of the other, hardly showing any difierences, 
except the strictly generic characters! This seems to be again one of 
those curious instances, so frequent in entomology, of the resemblance 
between the parasites and their hosts! By rearing a considerable 
number of galls of D. nehulosus, I obtained this species as well as its 
parasite almost in equal numbers. By cutting some of the galls open, 
I ascertained that a single specimen of the gall frequently contained 
both species^ thus setting aside a possible doubt whether these insects 
are not produced by two different, although closely similar galls. 
From the gall of D. custutaeformis I also obtained an Aulax (comp, 
below). 
The genus Aulax Hartig {^Aylax in Grerm. Z. II and III, A%ilax in 
vol, /F, p. 412) is not much better defined than Dia%tropliu&^ and I owe 
the determination of both to Dr. Bheinhard, in Bautzes, Saxony. 
Aulax^ according to Hartig, has the antennae 15 or 16 jointed (S ), 
14 or 15 jointed ( 9 )• The three species described by Griraud have 
all 14 ( S ) and 13 ( 9 ) joints. 
I have to add, however, that I can count only 13 joints in the 9 sjjecimens 
of 7). rubi, kindly sent me by Dr. Rheinhard. 
