352 NATURAL ARRANGEMENT OP INSECTS. 



have not yet solved. The first discovery of one of these 

 insects was made by Rossi, who found it upon the Po- 

 listes Gallica, and established for it the genus Xenos ; 

 and Mr. Kirby subsequently observed a Stylops emerg- 

 ing from its obtected pupa-case between the abdominal 

 segments of an Andrena. The whole structure of these 

 insects is very remarkable: their antennae are either au- 

 riculated, as in Sty lops; furcated,, as in Xenos; or flabel- 

 lated, as in Halictophagus ; and robust, compared with 

 the insects : their head transverse, with sub-pedunculated 

 eyes, consisting of comparatively few and separated hex- 

 agons. The mouth is of singular structure : the man- 

 dibles are apparently obsolete; it has no obvious labrum; 

 the labium and mentum are invisible ; and its trophi are 

 reduced to apparently a couple of setiform maxillae, with 

 an enormously large two-jointed maxillary palpus af- 

 fixed externally at their base ; the prothorax is trans- 

 verse and narrow ; the mesothorax also narrow, with a 

 couple of lateral distorted articulated appendages, the 

 analogues of elytra ; and the metathorax is very largely 

 developed, occupying more than one half of the insect; 

 and this gives room for the exercise of the large muscles 

 required for the movement of its expansive semicircular 

 wings, which fold longitudinally in repose, and rest 

 upon the body. These are without nervures, although 

 there is a slight indication of something like them, some- 

 what analogous to the irregularity of neuration we find 

 in the wings of the Coleoptera; and we strongly incline 

 to the opinion, that they have considerable analogy to 

 the eccentric genus Atractocerus, where we have also a 

 greatly enlarged metathorax, wings folding longitudi- 

 nally, and minute and all but obsolete wing-cases. The 

 tarsi of these insects vary in the number of their joints, 

 from two to four, and these are all furnished beneath 

 with a vesicular cushion, and they are without terminal 

 claws. These insects fly with a sort of undulating 

 motion, and are very conspicuous objects in the clear 

 sunshine. Their sexual differences are unknown ; 

 and it is assumed that those hitherto described are all 

 males, and that possibly the females are apterous: 



