6 PKOCEEDINGS OF THE NATIONAL MUSEUM vol. 69 



EXPLANATION OF NEW OR LITTLE USED CHARACTERS OF XYLOTINI 



Metasternum pilose or jmhescent. — This character in the Syrphidae 

 may be of specific, siibgeneric, or generic value. The metasternum 

 (posterior antecoxal piece) located between the middle and hind 

 coxae is either faintly pubescent or clothed with pile which approxi- 

 mates the length of the pile on the hind coxae. 



Metasfernal sdente divided. — In Trofidia each metasternal sclerite 

 is divided on its lower portion by a fairly distinct, narrow band of 

 membrane. 



Metasternal sclerites spurred. — The middle portion of each sclerite 

 is produced into more or less well-defined spur. Occurs in certain 

 males of Planes. 



Hind trochanter with spur. — This character occurs in the uiales 

 of certain species of Helophilus, Tropidia., Xylota., etc. It is usually 

 spoken of in keys and descriptions as " hind coxa with a spur," which 

 is erroneous, as the coxa is simple in all American forms of Xylotini 

 except in Aciochordonodes and Stilhosoma. 



Hind tihia toothed. — The hind tibia at apex on lower side may be 

 j)roduced into a single median tooth (Platies) or may be developed 

 into two teeth-like projections, one at each corner {Tatuoniyia.). In 

 other eases the lower apex may have a single tooth on the inner 

 corner {C lepidoniyia) or may be truncate {Eriophora) or there may 

 be a gentle concavity {jSterphus). 



Pleuroterglte loith ridge. — The pleurotergite is the sclerite which 

 iies between the attachment of the lower squama and the metathor- 

 acic spiracle. The ridge is a sharp one extending diagonally from 

 the spiracle upwards and backwards towards the anterior lower 

 corner of the scutellum. Occurs in Syritta and certain tropical species 

 of Planes and to some extent in some species of Tropidia. 



Fifth abdominal segment of female submeinbranous. — The females 

 of Tropidia appear to have the fifth abdominal segment reduced in 

 size, and much less chitinized than the preceding ones and more or 

 less retracted within the fourth. Syritta pipiens also shows this 

 condition to some extent and Syritta oceamca has it still more pro- 

 nounced. 



Head hroadJy elliptical or triangular. — The frontal aspect of the 

 head should be viewed. 



Face concave. — Face taken in profile. 



Lower face. — That part of the face lying between the lower eye 

 margin and oral margin. 



Ari^sta longer than width of face. — The width of the face taken 

 is that across its middle. 



Metathoracic spiracle smaller or larger than third antennal joint. — 

 It ma}- be noted that the two extremes occur in Xylotomima pigra 

 (smallest) and Xylota harhata (largest). 



