192 HYMENOPTEBA OF AMERICA. [PART I. 



1. Form lengthened. Metathorax prolonged horizontally behind 

 the post-scutel, then truncate vertically; offering above, in 

 the rear of the post-scutel, a sort of cavity limited poste- 

 riorly by a vertical plate divided by a fissure. First abdo- 

 minal segment entirely sessile, wide, distinctly truncate 

 anteriorly, so as to form a sharp transverse ridge, its 

 suture indistinct, especially in the middle. Vertex of the 

 females offering two little mammae filled with hair. JIales 

 nearly as large as the females. 1 



(Group of the 0. quadrisectus.) 



(Sauss. Vespides, I, p. 145, Sect. 21. — Division Pseudodynerus. 

 Ibid. Ill, 22n.) 



30. A. Aztecus Sauss. — Gracilis, niger, nitidus, grosse foraminato- 

 punotatus ; vertice arcubus duobus penicillatis instructo ; inetanoto 

 pone post-scutellum producto, postiee foveolato, supeme cristulam per 

 fissuram divisain ferente ; abdomine dense punctato ; antennis subtns 

 ferrugineis, scapo flavo-lineato ; mandibulis, tiliiis anticis, puncto fron- 

 tali ; clypeo J lineolis 4, % omnino, pronoti et abd. seginentoruui 1, 2 

 margine, post-scutello, macula subalari, metanoti punctis 6, et primi 

 segtni'iiti puncto utrinque, luteis; alis infuscatis violaceis. 



Odgncrus Aztecus Sauss. Revue de Zool., 1857, 275. 



Total length, 15 mm. ; wing, 15 mm. 



9. A species closely allied to the 0. i-sectus, having the same 

 form, bill smaller. Clypeus pyriform, very coarsely punctured, 

 with a depressed point, and carrying toward the apex a vertical 

 groove Eead and thorax polished, cribrose with great holes. 

 On the vertex, behind the ocelli, one sees two tubercles of brown 

 hair; or a double bush of hair surrounding a, smooth space. 

 Anterior border of the prothorax slightly concave; its angles 

 sharp. Metathorax not retracted behind; its superior face 

 cribrose with strong punctures like the remainder of the thorax. 

 Its concavity smooth, excavated, finely punctured, with blunted 

 borders, except, at its superior extremity, where it is terminated 

 by a little vertical plate. Abdomen quite slender; its first seg- 



1 In the third volume of my Etudes sur la Fam. de Vespides, p. 220, I 

 have placed in this Division the 0. luctuosus, but it would be better placed 

 in the Subgenus Odynerus. (See below the corresponding Section formed 

 by this species ) 



