14 BULLETIN 31, UNITED STATES NATIONAL MUSEUM. 



describe. The lengths of the joints of the antennee offer characters of 

 some vahie, bat I feel sure that they are not so reliable as some authors 

 have supposed. lu a rather large series of specimens, all apparently 

 belonging to the same species, 1 find a very considerable variation in 

 the length of the third joint, as will be seen in figure oa, plate I. 



TABLE OF SPECIES. 



1. — The lateral margin of the third abdominal segment yellow .2 



The lateral margin not yellow 3 



2.— The black on the fifth abdominal segment is shaped like an inverted V. laterale 



The black has the two posterior branches arcuate, and widely separated at the 



tips ypsilon 



3. — Arcnate bands of abdomen entire ; the black spot on the fifth segment is elon- 

 gated and narrow, with the branches nearly parallel .... integre 



Arcuate bands interrupted ^ 



4. — Eastern species ^ 



Western species derivatum 



5.— Black spot of the fifth abdominal segment inverted Y-shaped . . veutricosum 



Black spot, etc., inverted V-shaped pubesceus 



Clirysotoxuin laterale. 



Cliri/sotoxum laterale Loew, Centur., v, 42. 



Habitat. — New York !, Nebraska (Lw.). 



S . Length, 11'""'. Second joint of antennae a little longer than the 

 first ; third joint a little longer than the first two together ; eyes pilose. 

 Lateral stripes of the thorax sub-entire ; the white vittulte conspicu- 

 ous. Scutellum yellow, the disk black fasciolate. Yellow fascite of the 

 abdomen arcuate, very narrowly interrupted, connected with the yel- 

 low border of the lateral margins ; posterior margin of each segment 

 jellow; on the 'first' segment narrowly, on the third broadly, on the 

 fourth strongly dilated, on the fifth produced into an oblong spot, so 

 that between this spot and the fascia tlie black forms an inverted Y. 

 Hypopygium yellow. Each of the middle segments of the venter with 

 narrow abbreviated yellow fascia on the posterior margin. Legs wholly 

 yellow. Wings cinereous hyaline, costa with a narrow fuscous cloud of 

 equal width. From G. derivatum Walker, to which this is nearly re- 

 lated, it will be easily distinguished by the thoracic stripes being broader, 

 by the margin of the abdomen Deing yellow, by the picture of the 

 venter being different, and by the legs being wholly yellow.— Transla- 

 tion. 



A single female from New York (August 25) I identify as this, but the 

 first segment of the abdomen does not have a posterior yellow margin. 



Chrysotoxum ypsilon, u. sp. 



Habitat. — New Mexico!. 



$ . Length, 10 to 12""". Large. Third joint of the antennae longer 

 than the other two together. Scutellum on its disk dark and translu- 

 cent. Arcuate bands of abdomen rather broad, connected with the yel- 



