a Family of the Hymenoptera Heterogyna.] 267 



lated within, and two submarginal cells, the first of which is smaller 

 than the second, and receives the recurrent nervure at nearly three- 

 fourths of its length. 



Legs short and slender : coxce robust, canaliculated above for the articula- 

 tion of the femur : trochanter not distinct : femora and tibice slender 

 and subcylindrical, the latter furnished at their apex with a single 

 calcar : tarsi slender, longer than the tibiae, the basal joint as long as 

 the three following, the fourth joint the shortest : the claws simple. 



Abdomen elongate, curved downwards, cylindrical and slightly clavatej the 

 dorsal segments, but especially the terminal ones, slightly constricted ; 

 the penultimate segment much shorter than the antepenultimate, and 

 forming merely a transverse slip ; the first segment, which forms the 

 peduncle, quadrate, the angles rounded; above deeply channeled down 

 the middle, which gives it a bilobate appearance, beneath carinated 

 and flattened laterally from this carina : the apical segment obtuse 

 and rounded. Type of the genus JEnictus ambiguus, Shuck. 



Named from its senigmatical structure, which participates in that 

 both of Labidus and Dorylus, from the latter of which, although the 

 neuration of the wings is nearly similar, other parts differ so much, 

 especially the mandibles, prothorax, peduncle of the abdomen and 

 legs, that it would not consistently associate with it, and in all these 

 particulars it completely agrees with Labidus, forming a link between 

 the two genera which thus corroborates their affinity*, although 

 their generic disparity is strongly substantiated by the comparative 

 conformation of the male sexual organ, which, as in Dorylus, here 

 also has the fornicate lateral valves (the external sheath), which are 

 also fimbriated at their apex. The central process (penis), however 

 here takes the same curve, but higher than these valves, which closely 

 embrace it laterally, and are not more than three-fourths as long as it ; 

 this central portion forms, viewed from above, a double parallel 

 tube, separated by a narrow fissure at its extreme apex, but after- 

 wards joined by membrane : the representative of the inner sheaths 

 take here a very different form from what they present in Dorylus, 

 for here they are fornicate, excised just within their apex, they then 

 become suddenly dilated, terminating abruptly in an obtuse angle, 

 which points downwards. The horizontal furcate plate beneath is 

 very broad and quadrate, the furcation being formed by two slender 

 acuminated converging spines. This remarkable insect is a na- 



* St. Fargeau hints a doubt of this, where he says, " Je ne presume pas, 

 en T absence du sexe feminin, quelle peut etre leur place definitive, et, du 

 reste, l'analogie apparente me porte a les laisser avec les Dorylus, et a les 

 placer ici hors de rang, en attendant des eclaircissemens sur leurs mceurs." 

 ■ Hist. Nat. des Hymenop.' (Suites a Buffon), torn. i. p. 227. But this au- 

 thor has made many mistakes throughout his notice of these genera, and 

 his opinion of them consequently is not at all to be trusted. 



