8 AMERICAN HYMENOPTERA. 



less distinct lateral carinas which usually connect it with the 

 mesonotum in front and sometimes unite behind. In some 

 species these carinae are high and the front of the scutellum 

 appears deeply excavated, in others they are indistinct. 



The broad mesothoracic pleura lies below the anterior wing, 

 its posterior edge being frequently crenulate or keeled, the 

 suture running obliquely from the base of the anterior wing 

 to the posterior edge of the mesocoxa, where a small projec- 

 tion articulates with a similar one from the metapleura and 

 apparently serves to prevent too great flexure of this seg- 

 ment of the leg. There are no sutures or other marks be- 

 tween the pleura and sternum, and I have observed no 

 characters on the latter which are useful in distinguishing 

 species. 



Metathorax. — The metathorax proper is a narrow band 

 which lies directly behind the mesothorax, bearing the poste- 

 rior wings above and the posterior legs below. It has no 

 distinctive characters and is so closely joined to the median 

 segment — which I have everywhere referred to as the meta- 

 thorax — that I have not mentioned it in descriptions. It con- 

 sists of a narrow dorsal band, composed of the pleura and 

 postscutellum, partly separated by the insertion of the poste- 

 rior wings, and a narrow ventral section — epimeron — extend- 

 ing back below and closely attached to the median segment 

 and bearing the posterior legs behind. 



Median segment. — The median segment, or, as I have every- 

 where called it, the metathorax,* is rounded, sometimes with 

 the back part of the metathorax proper almost globular, 

 but generally more or less flattened behind and sloping to 

 the insertion of the abdomen. In the Genus Ophiopterus, 

 however, it is produced behind into a distinct neck. The 

 surface is smooth, more or less strongly, finely or coarsely 

 rugose, rugose-striate or reticulate or rarely almost granulose. 

 A more or less distinct median longitudinal furrow fre- 

 quently runs from the insertion of the abdomen to the poste- 

 rior edge of the metathorax proper, but in some species this 

 is wanting. 



* In all descriptions of American species of this tribe, it has been 

 referred to as the metathorax and a change would lead to confusion. 



