172 PASSALCECUS. 



3. Diodontus tristis. 



D. ater ; incisura inter mesothoracem et scutellum consuta ; an- 

 tennis pedibusque atris. 



Pemphredon tristis, Van d. Lind. Obs. ii. 76. 1. 

 Diodontus tristis, Shuck. Foss. Hym. 187. 3. 



Dahlb. Hym. Europ. 249. 149. 



Wesm. Hym. Foss. Belg. 120. 1. 

 Diodontus pallipes, Dahlb. Hym. Europ. i. 250. 151 $ . 



Female. Length 3J lines. Black and shining; head large, 

 subquadrate, wider than the thorax, finely punctured, most 

 closely so on the face ; the mandibles obscurely ferruginous at 

 the apex. Thorax : the disk finely punctured ; the deep channel 

 which separates the scutellum from the mesothorax with a 

 number of transverse elevations (consute) ; the metathorax very 

 coarsely rugose ; the wings hyaline and splendidly iridescent ; 

 the nervures piceous, the stigma blackish ; the tarsi sometimes 

 obscurely rufo-testaceous ; the calcaria testaceous, the inter- 

 mediate and posterior tibiae spinose. Abdomen ovato-conic, 

 and very delicately punctured, the apex obscurely testaceous. 



Male. Length 2i lines. Differs in being more strongly punc- 

 tured on the head and thorax ; the face silvery ; the anterior 

 tibia3 in front, the posterior pair at their base, the anterior tarsi 

 and basal joint of the intermediate and posterior pairs, yellow, 

 the latter obscure. 



An abundant species in the London district, and generally 

 distributed; it preys upon Aphides, and forms its burrows in 

 dead twigs of the Bramble, Rose, &c. 



Genus 7. PASSALCECUS. 



Pemphredon, pt., Van d. Lind. Obs. ii. 79 (1829). 

 Diodontus, pt., Curtis, Brit. Ent. xi. 496 (1835). 

 Xyloecus, Shuck. Foss. Hym. Consp. Gen. (1837). 

 Passaloecns, Shuck. Foss. Hym. p. 188 (1837). 



Head subquadrate, wider than the thorax ; eyes ovate ; ocelli 

 in a triangle on the vertex ; antennae inserted at the base of the 

 clypeus, not approximate ; clypeus transverse, tridentate, some- 

 times obsoletely so; the labrum entire. Thorax sublinear; 

 collar transverse, slightly constricted into a sort of neck ; meta- 

 thorax elongate, obtuse at its extremity ; the anterior wings with 

 one marginal cell acuminate at its apex, and with two submar- 



