10 HEAD. 



one-half of tlie width of the eye ; vertex slightly depressed below 

 the level of the eyes ; facial pit deep, undivided by a septum, 

 extending to the oral margin, which is up-turned and prominent ; 

 cvirved suture (Bogennaht of Brauer and von Bergenstamm) 

 ending in a pit above the lower margin of the eye, the pit on 

 each side being prolonged into a more or less marked, shallow 

 depression (^transverse impression of Hough) separating the face 

 from the jowls ; * the latter narrow in front, broad and rounded 

 posteriorly, crossed by a line of black bristles which passes on to 

 the occipital surface of the head, and is continued as the series 

 of small bristles marking off" the posterior orbits ; jowls clothed 

 with fine hair behind the line of black bristles just mentioned, in 

 front, like the face, bare ; vibrissal ridges sharp and nari'ow, not 

 broadening out below as in Stomoxj/s, Haeniatohia, and other 

 genera of Muscinae, ciliated to the level of half the length of the 

 thii'd joint of the antennae, or higher ; vibrissae small, fine, no 

 elongated or conspicuous vibrissa even on the vibrissal angle, 

 which is widely separated from the oral margin. Under side of 

 the roof of the buccal cavity with two large, dark brown, strongly 

 chitinised patches, very conspicuous in the majority of species 

 when the head is viewed from below. Eyes bare, in both sexes 

 the facets in front towards the inner margin conspicuously lai"ger 

 than those behind. First two joints of the antennae small, the 

 third long, nearly reaching the oral margin, concave in front, the 

 tip being produced into a prominent forwardly-directed angle. 

 On the inside of the third joint of the antenna near the base a 

 minute though well-marked pore can usually be distinguished, 

 constituting the orifice of a sense-organ (see Fig. S).'\ Arista 

 three-jointed, though first two joints very small, and first joint 

 visible only when the antenna is removed and examined under 

 the microscope ; terminal joint remarkably broad throughout its 

 length, flat, tapering somewhat to the tip, but far from being 

 reduced distally to the proportions of a fine hair, as in the case 

 of the arista of Sfomoxj/s ; feathered on the upper side alone 



* I follow Mr. G. H. Yerrall ("British Flies, Syrphidae, etc.," 1901) in 

 using the term joivl for the part of the head beneath the eyes [Dacke, of 

 German authors), separated from the face (German, Wange) by the curved 

 suture or its prolongation. In 1898 Hough (" Proc. Acad. Nat. So., Phila- 

 delphia," 1898, p. 168) proposed the terms gciia and bucca for Wange and 

 Backe respectively. 



t Dr. Stuhlmann, writing of G. brevipalpis, Newst., calls this an 

 "auditory" organ. If the antenna be mounted in glycerine and ex- 

 amined under a low power, the sense-organ has the appearance of an 

 oval sac. 



