PROCEEDINGS OP THE NATIONAL MUSEUM 



the basis of antennal characters. One, typified by hicinctum (Lin- 

 naeus), genotype of Chrysotoxum, has the first and second antennal 

 joints greatly elongate, the two combined being much longer than 

 the third, or the arista. This appears to be the dominant group in 

 Europe and also occurs in Asia, but no species are known from 

 America. The second subgenus, Prhnochrysotoxum, new subgenus 



(type, ypsilon Williston), has the first 

 and second joints but little elongate, 

 their combined length approximating 

 the length of the third and frequently 

 being much shorter. The entire length 

 of the antenna is often much shorter 

 than the length of the fore tarsus. The 

 specific character which appears to be 

 of most importance in the subgenus 

 PHviochrysotoxum is found in the apical 

 corners of the second, third, and fourth 

 tergites. In one group of species they 

 are projecting and in the remaining spe- 

 cies the corners are confluent with the 

 side margins of the abdomen. In the 

 former group the females usually have 

 the apical corners of the fifth tergite 

 likewise projecting. Also in the first 

 group the third antennal joint is usually 



Figs. 1-3.— 1, inxer view of the about three times the length of the first, 



ANTENNA TO SHOW KELATIVB , • ,i n •. • i . 



LENGTH OF JOINTS OF: a. cHRYs- wficreas lu the second group it is about 



oToxuM (Primochrysotoxom) ^^]_^q ^lie leuffth of the first. 



The male genitalia are very uniform 



VENTRICOSUM LOEW, h. CHRYSO- 



T o X u M (Primochrysotoxum) 



YPsiLON WILLISTON, c. chryso- • , sDccies of thc o-euus Two 



TOxuM (Chrysotoxum) bicinic- ^^^ iiiobu bpecieb ox iiie ^exiuh. j. vvu 



TUM Linnaeus. 2, Abdomen of species, at least, are notable exceptions, 



Chrysotoxum (Primochryso- -, . tt • /-m \ i 



TOXUM) VENTRICOSUM LoEw, FE- namely, cautum Harris (Europe) and 

 male, showing the even OUT- tubercuUtum, new species (China). In 



LINE. 3. Abdomen of Chryso- .•,■,,, .^ ,i j-i 



TOXUM (Primochrysotoxum) yp- the latter the styles are asymmetrical, 

 siLON Williston, female, show- but this asymmetry is of a different type 



ING THE projection OF THE p j.1 j. 1. • 1 T_ i. • j.1 



APICAL CORNERS OF THE TERGITES ^^om that which charactcrizes the mem- 

 bers of the subfamily Sericomyinae. 



Abnormal development of the abdominal segments appears to be 

 unusually frequent in members of this genus. A large number of 

 specimens examined had one or another segment more or less doubled 

 by the presence of an additional rudimentary segment. 



The species of Chrysotoxum are chiefly Holarctic in distribution. 

 They are very partial to woodlands and are usuall}'^ found on the 

 forested slopes of mountains. A few species are known from tropical 



