J. H. MERRILL 127 



extends backward between two parallel, longitudinal, yellowish-white bands 

 on the mesonotum to the mesoscutellum. The center of the rnesoscutellum 

 has a square yellowish-white spot on it, and is interrupted at its front margin 

 by a dark one. The posterior margin of the entire plate has a narrow white 

 line, the remainder of the plate is black. On the metascutellum (generally 

 called postscutellum) is an oblong yellowish-white spot. Both front and 

 rear margins of this plate have a yellowish-white Une, each side is black and 

 a black line crosses from one side to the other just in front of the oblong spot. 

 The mesosternum and metasternum as well as their pleura are pale rufous. 

 The tegula, a raised spot beneath the fore wing and another spot below this 

 are yellowish-white. The uotum of the propodeum is dark with a yellowish- 

 whitre spot separating it from the rufous pleura at its posterior end. The legs 

 are pale rufous, with the knees, tibiae and tarsi whitish. The exterior surface 

 of the middle tibiae and tarsi as well as the tarsal tips and sutures are darker. 

 In the posterior tibiae the outer extremitj' is darkened and the tarsal segments 

 become darker toward the tarsal claws, which are brownish-black. The wings 

 are hyaline with dark brown nervures. The stigma is pale fuscous at its 

 base but becomes darker towards its apex. The areolet is petiolated and the 

 recurrent nerv'ure enters it in the middle. 



The abdomen is dark brown, pohshed and transversely aciculated above, 

 and obhquely aciculated at the sides. On the notum of the second segment 

 is a broad, dorsal depression extending from the base nearly to its tip. On 

 the third, fourth, fifth, sixth, seventh and eighth segments are roundish, 

 3'ello wish-white spots, which on the last two segments become elongated, 

 with their axis at right angles to that of the bod3^ The venter is yellowish- 

 white with brown bands. The ovipositor is of a reddish-brown with darker 

 colored sheaths. 



]Male unknown. 



Megarhyssa humida is more apt to be confused with Rhyssa 

 persuasoria than with any other species, yet an examination of 

 the sternal plates will show a marked difference. The fact 

 that the pleura and sternum of the second abdominal segment 

 are fused for a short distance will serve to distinguish it from 

 Rhyssa persuasoria. The fact that the mesosternum and meta- 

 sternum of M. humida are rufous and not l^lack is another dis- 

 tinguishing character. It can be distinguished from M. atrata 

 by the absence of the yellowish-white markings found on the 

 latter. It can be distinguished from Megarhyssa norionii, 

 canadensis, lunator, greenei, and mexicana by the presence of its 

 yellowish-white orbits. 



This species was described by Saj- as Pimpla humida and was 

 later put into the genus Rhyssa by Walsh, but the structural 

 characters of the sternal plates, the fusion of the pleura and 

 sternum of the second abdominal segment, the ends of the 



TRANS. .VM. ENT. SOC, XLI. 



