AMERICAN HYMENOPTERA. 17 



A MONOGRAPH OF THE TRIBE BAI^iSIXI. 



BY G. C. DAVIS. 



This tribe is characterized primarily by the forni of the mandibles, 

 which have the superior tooth divided or notched at the tip, so that 

 in appearance there are three teeth to each mandible. It is further 

 characterized by having the head broader than deep, clypeus sepa- 

 rated ; antennee filiform, composed of from twenty to twenty-five 

 joints, the first one cup-shaped, irregularly and diagonally truncated, 

 the second much smaller, considerably inserted in the first, the third 

 cylindrical and longer than those following it, thorax short, broad, 

 narrowing gradually posteriorly ; abdomen broadly sessile, composed 

 usually of six segments, the first of which is often traversed by two 

 longitudinal carinjie, and sometimes the first two or three segments 

 are crossed by a transverse groove ( genus Bumus) ; ovipositor short, 

 often not exserted. The general form is short and thick set, though 

 the smallest species (geiuis Promethi(s) are more slender. The sexes 

 differ by the % being smaller and less robust ; they also differ in 

 color markings, the most notable of which is the entire yellow face 

 of the S , never found in the 9 , fintl in the other yellow markings 

 which are more largely develoj^ed in the % than in the 9 . 



In the immature stage, Bassini are well known as parasitic on 

 Syrphus fly larvae. The individual host of the various species seems 

 to be unknown. In our rearings, Bassus scutellaris was bred from a 

 Syrphus larva on rag weed, August 31st, and we have reared Bassus 

 Icetatorius, Syrphodonus agilis and Promethus costalis from Syrphus 

 larvje feeding on Aphis brassicce. To Mr. Ashmead we are indebted 

 for the note on finding Bassus orbitalis and Syrphodonus pacificus 

 parasitic on Syrphus larvae feeding on the same. He also reports 

 the rearing of both sexes of Syrphodonus pleuralis from a Syrphus 

 puparium on rose. The species do not seem to confine themselves to 

 any one species of Syrphidte. Mr. Cresson has a % and 9 of Syr- 

 phodonus agilis reared from a species of Sphcerophoria, while this 

 year we have reared the same species from quite a different puparium 

 taken on willow. We have reared Bas.^us la'titorius from several 

 entirely different puparia. In Europe B. hdatorius has been found 



TRANS. AM. ENT. SOC. XXII. (3) FEBRUARY, 1895. 



