372 [May 



genus ; the first segment is longitudinally striate ; the second conceals 

 all the following in both sexes. The antennae are 15-jointed (S ) and 

 13 or 14-jointed ( 9. ). The seven known North American species have 

 the polished spot on the pleurae aciculate; in S. mendax this sculpture, 

 although very faint, also exists. The species of Ceroptres known to 

 me, have these spots perfectly smooth ; this difference between the two 

 genera may however not prevail through all the species, as Hartig 

 places Ceroptres among the species with aciculate pleurae. The sheath 

 of the ovipositor is much less projecting above the ventral line in this 

 genus than in Ceroptres. 



The first segment of the abdomen usually appears somewhat tumid, 

 as was already noticed by Hartig (abdomen collo striata, tumido, says 

 he) ; but it seems to me that this appearance is merely an optical illu- 

 sion, produced by the presence of the striae. The face is aciculate. the 

 striae converging towards the mouth ; but as this character seems com- 

 mon to all the species, and in fact, to a great many Cynipidse. it has 

 been omitted in the descriptions. 



The species of Synergus are very numerous in Europe and rather 

 difficult to distinguish, being not only very uniform, but also very vari- 

 able, in their coloring; it has been observed, however, that in the spe- 

 cies of mixed coloring (black and yellow), certain parts of the body 

 only are subject to variations, others preserving, on the contrary, a very 

 constant coloring. The principal characters have to be derived from 

 the shape of the body, especially of the abdomen, and from the sculp- 

 ture of the thorax. Hartig also adverts to frontal ridges immediately 

 above the eyes, which, in some species, reach the vertex, in others run 

 only a very short distance. I distinctly perceive very short ridges of 

 this kind in S. oneratus and S. campanula, but characters of such ex- 

 treme delicacy are apt to mislead, as their perception is too dependent 

 on optical conditions. 



The following arrangement of the seven known North American 

 species applies principally to females, the males of some of the species 

 not being yet discovered Cynips quercus lana Fitch, Rep. II, No. 

 31G, apparently likewise a Synergus, but unknown to me. has not been 

 included in this table. 



1. Prevailing color of the body yellow 



Prevailing color of the body black 3 



2. Antenna! joints 3 and 4 of nearly equal length ; 1 



mesonotum reddish-yellow, with a more or I L s _ oneratus Harris p. 

 less broad, sometimes obsolete black stripe in 

 the middle: antennse ( 9 ) 14-jointed. J 



