162 HYMENOPTERA. 



abdomen is pedicelled, and differs from Mimesa, a still more 

 slender-bodied genus, in having the tip of the abdomen more or 

 less grooved, while in Mimesa it is flat and not grooved at all. 

 Psen leucopus Say has a dense silvery pile on the front of 

 the head, with black antennae, and the pedicel is rather short. 



NYSSONID^E Leach. In this family the head is transversely 

 longer and less cubical than in the preceding group ; the ver- 

 tex is higher and more convex, while the front is narrow, the 

 clypeus long and narrow, the eyes long and narrow, and the 

 antennae are more clavate than in the Crabronidoe, and 

 the propodeum is sometimes armed with acute spines, while 

 the enclosed space is smoothly polished or striated. The wings 

 are long and narrow, and the abdomen is sessile in the typical 

 genera, where it is obconic, but clavate when pedicellate. 



In Trypoxylon the body is long, with a pedicellate clavate 

 abdomen. In Europe "Mr. Johnson has detected it frequent- 

 Ing the holes of a post pre-occupied by a species of Odynerus, 

 and into which it conveyed a small round ball, or pellet, con- 

 taining about fifty individuals of a species of Aphis ; this the 

 Odynerus, upon her return, invariably turned out, flying out 

 with it, held by her legs, to the distance of about a foot from 

 the aperture of her cell, where she hovered a moment, and then 

 let it fall ; and this was constantly the case till the Trypoxylon 

 had sufficient time to mortar up the orifice of the hole, and the 

 Odynerus was then entirely excluded ; for although she would 

 return to the spot repeatedly, she never endeavored to force 

 the entrance, but flew off to seek another hole elsewhere." 



T. politum Say has purplish wings, and no enclosure on the 

 propodeum. 



T. frigidum Smith lives in the stems of Syringa, from which 

 it has been reared by Mr. Angus. The thin, delicate cocoon is 

 long and slender, enlarging slightly towards the anterior end. 



The genus Mellinus (belonging to the third subfamily, Mel- 

 linince,) is known by its broad front, and slender antennae, 

 and its pedunculate abdomen, while in Alyson, a slender- 

 bodied genus, it is sessile. Mellinus bimaculatus Say has a 

 black head, with pale tipped antennae, and two ovate yellow 

 spots on the abdomen. Atyson oppositus is black, with two 



