216 AMERICAN HYMENOPTERA. 



the head is located at the center of a circular concavity which 

 permits of a free movement of the head on the body. The 

 occipital foramen is rectangular or rounded in general form, 

 its long axis being the vertical one. The anterior ends of 

 the two episterna of the prothorax forms knobs which loosely 

 articulate with the occipital region of the head. The neck 

 membrane on the dorsal side is attached to the lower sur- 

 face of the pronotum. 



The pronotum is so separated from the rest of the pro- 

 thorax that it almost appears to belong to a separate seg- 

 ment. It forms a collar completely encircling the front of 

 the mesothorax and extends backward on each side in the 

 form of a large lobe which reaches the tegulae. This lobe 

 acts as a protective shield, covering the first thoracic spira- 

 cle. The notum is divided by a transverse groove or depres- 

 sion into an anterior and a posterior part. The former is 

 sometimes called the scutum and the latter the scutellum. 

 The scutellum is densely pilose, but the scutum has very 

 much less hair. The propleura are large, oblong plates, 

 presenting both lateral and ventral surfaces. They are re- 

 tracted beneath the notum so as to be at most only partly 

 visible laterally. Each pleuron appears to be made up of a 

 single piece, which is apparently the episternum. The pros- 

 ternum is a small, partly invaginated plate. It is widest in 

 the middle and narrows to an acute angle both in front and 

 behind. Its surface is often longitudinally striate in the 

 middle. 



Mesothorax. — The mesonotum consists of three plates. Of 

 these plates, only two, the scutum and the scutellum, are 

 visible with the plates in their natural position. The scutum 

 is the large anterior plate which extends from the pronotum 

 back to opposite the bases of the hind wings. Its anterior 

 corners reach under the prothoracic lobes slightly. It has a 

 very narrow strip on each side which appears to be partially 

 separated from the main part by a suture. The scutum, as 

 a whole, is widest anteriorly. Its front margin curves for- 

 ward somewhat ; the side margins are somewhat incurved 

 and the hind margin is broadly curved backward. Its sur- 



