210 NORTH AMERICAN SCELIPHRON (HYMENOPTERA) 



Mesothorax. — The mesonotiim is a broad, rather sellate plate, 

 with its anterior margin articulating with the posterior margin 

 of the collar and at the sides with the prothoracic lobe. Its 

 lateral margins are somewhat emarginate to receive the tegiilae 

 and slightly reflexed, while its broadly truncate posterior margin 

 is closely applied to the seutellum. Lying between the lateral 

 margin and the median line on each side is a shallow groove 

 starting from the posterior margin and extending forwards for 

 about one-third the length of the mesonotum. Near the anterior 

 end of each groove there is a curved incised line extending for- 

 wards for the middle third of the segment. These curved lines 

 may be the parapsidal grooves. A short straight line can be 

 seen lying along the anterior third of the median depression of 

 the mesonotum. The seutellum is a rather narrow plate lying 

 behind the mesonotum. It is distinctly raised in the middle and 

 usually marked by a faint median depression. It has a lateral 

 forward extension on each side, as far as the base of the fore wings 

 and tegulae, broken by two deep cavities, a smaller one on each 

 side of the raised central portion, and a larger cavity from which 

 the fore wings have been evaginated. These two cavities are 

 separated by a sharp ridge. The mesopleuron is a large plate 

 occupying the side of the mesothorax and extending obliquely 

 from behind the prothoracic lobe to the base of the mesocoxa, 

 where it ends in an elevation evidently serving to prevent further 

 dorsal flexure of the leg. The mesopleuron is bounded dorsally 

 by part of the mesonotum, and by the overhanging edge of the 

 seutellum, but its ventral limits are not defined. Its anterior 

 margin shows a deep depression under the prothoracic lobe bear- 

 ing a spiracle, which is protected by the lobe, but its posterior 

 boundaries are rather vague. 



This plate is divided by morphologists into three parts, the 

 pre-episternum, the episternum and the epimeron. The epister- 

 nal groove is a shallow lateral depression marked by scattered 

 ridges and separating the pre-episternum from the episternum. 

 The epimeron has no definite limits, but lies in the broad depres- 

 sion extending oblifiuely down the sides of the body and mark(>d 

 by distinct foveae. This depression is known as the metapleural 

 groove. 



