120 GENERA OF HYMKNOITERA. 



The peculiar neurntion of this beautiful genus will readily distin- 

 guish it from all others in the Division. Of the three sjHM-ies that 

 have Injen described jw occurring in our fauna, tdulomintiUx and rufi- 

 nodus apf>ear to be common where they occur and are handsome 

 insects ; the former has the abdomen entirely red, the first segmeru 

 not nodose at apex, while in the latter siK'cies the first segment only is 

 red, distinctly nodose at ajK'x and the renuiining s(>gments ornamented 

 with white ; biinacntutiiii apjKjars to be exceeilingly rare, anil has not 

 yet been seen by the writer. 



Family PEMPHREDONIDiE. 

 Table of Genera. 



Anterior winjrs without iv tiiird discoidal cell aud therefore only one reeurrent 

 nervure; Hti^fuui. unusually large. 

 Abdomen suhsessile ; recurrent nervure joining; the first transverse cubital 



nervure Npilomena Shuck. 



Abdomen petiolate ; recurrent nervure received in middle of first sul)nmrj{inal 



cell NtlgniUH Jur. 



Anterior wings with three complete discoidal cells and therefore with two recur- 

 rent nervures. 

 Abdomen distinctly jtetiolate; head and thorax more or less hairy. 



Fii-st submarginal cell receiving both recurrent nervures, sunietinies the 



se(;ond recurrent nervure is almost interstitial C'emoilUM Jur. 



First and second submarginal cells each receiving a recurrent nervure. 



Pemphredon r^atr. 

 Abdomen subsessile or with very short petiole; head and thonix not hairy; 

 first and second submarginal cells each receiving a recurri'it nervure. 



Posterior tibite unarmed ; labrum pointed at tip Passaloe '•un Shuck. 



Posterior tibiie spinose or subserrate; labrum emarginate at tip. 



Diodontus Curtis. 

 This family is composed of slender, shining black sj)ecies, mostly 

 small in size, the anterior wings with two submarginal cells, the fiii<t 

 being two or three times longer than the second, which is rectangular. 

 Spihmena and Stlgmus are remarkable for the unusually large 

 stigma and the absence of the third discoidal cell ; the marginal cell 

 is much narrowed to the apex, which is acutely pointed ; the alxlo- 

 men has a long slender petiole in StigiiiKS and subsessile in Spilotnenu. 

 The species are quite small, and only three have l)een described. 



Cemonus and Pemphredon are very closely allied to each other, and 

 have been united by some authors. They differ chiefly in the neura- 

 tion of the anterior wings as indicated in the above table. The ab- 

 domen has a long, flattened petiole. Only one species in each genus 

 has been described. 



