ART. 9 AMERICAN XYLOTINE SYKPHID-FLIES SHANNON 45 



mesonotum fiat, bronzy black with short yellowish pile and a pair 

 of faint median stripes; fore and mid legs with fetnora black, yellow 

 at bases and tips ; tibiae brownish yellow ; tarsi pale j^ellow, the last 

 two joints blackish; hind femur black, moderately swollen for the 

 genus; tibia brownish, arcuate with apical spur; tarsus pale brown, 

 last joints darker; abdomen slightly constricted at second and third 

 segments, each of which bears a pair of small yellow spots; wings 

 smoky; discal cross vein at middle of discal cell, but little oblique; 

 petiole beyond first posterior cell as long as discal cross vein; 

 squamae and halteres pale. Length, 6.5 mm. ; wing, 5 "mm. 



Tyye locality. — I von Beni, Bolivia (February, 1922, William M. 

 Mann, while on the Mulford Biological Expedition). 



Type.—C?ii. No. 27859, U.S.N.M. 



Nearest related to vagans (recorded above). The front is nar- 

 rower, the mesonotal stripes much less distinct, and the hind femur 

 less swollen. 



Genus STILBOSOMA Philippi 



Genotype. — StUbosoma rubiceps Philippi (by present designation). 



STILBOSOMA RUBICEPS Philippi 



Several peculiar features characterize this species. The body is 

 entirely dark except for the reddish yellow front and face; the an- 

 tenniferous projection is very prominent, causing the face to be 

 deeply concave ; the eyes of the male are nearly as widely separated 

 as in the female; the antennae are large, the third joint much larger 

 than the "metathoracic spiracle; arista as long as width of face; 

 thorax and abdomen broad ; metasternum bare ; hind coxa with small 

 spur ; hind trochanter simple ; hind femur enlarged with a bidentate 

 projection at apical, ventral, and outer position; all the puvilli and 

 bases of claws whitish, the posterior ones large; discal cross vein 

 joining discal cell far beyond middle and bearing a free-ending 

 branch ; first posterior cell closed practically at the wing margin. 



The presence of a spur on the discal A^ein is unique in the Syrphidae, 

 and Mr. Curran has opened an interesting question concerning its 

 origin. Mr. Curran writes :'' "The anterior cross vein in the Syr- 

 phidae, or at least some of them, is not wholly a cross vein but is a 

 fusion of what is termed the fifth radius and the cross vein. This 

 may not be true in the Muscoid groups, but we have no proof that it 

 is or is not, but it is certainly true in the Syrphid genus StWbosonia 

 Philippi from Chile." 



The discal cross vein leaves the third vein in a very diagonal 

 direction which gives it the appearance of a typical Rg forking in 



«54th Report Ent. Soc. Ontario, p. 21, 1923. 



