EEAX. 203 



black bristles with longer bristles between them, this crest scattering posteriorly behind the suture into a 

 cluster of sparse black bristles, between which, in front of the scutellum, a more or less distinct tuft of 

 short, white hairs is visible ; scutellum with short white hairs in the middle, and a row of long black 

 bristles along the edge. Abdomen : segments 2-4 black in the middle, their lateral and posterior margins 

 broadly grey ; segment 5 silvery, with a black spot in the middle, seldom wanting ; segments 6 and 7 

 silvery ; forceps rather large, black, the lower half nearly as stout as the upper half (like t. 2. f. 8 in 

 Bellardi), and with a brush of black hairs, more or less mixed with paler ones, on the underside. Legs 

 beset with whitish hair and the usual black and pale bristles ; front coxse with a fringe of white hair ; 

 femora black, with a greenish metallic lustre ; tibiae red, darker at the tip ; tarsi red. Halteres yel- 

 lowish, with a brown knob. "Wings with an almost imperceptible brownish tinge ; costa slightly, but 

 distinctly, expanded and thickened beyond the end of the auxiliary vein, the corresponding part of the 

 costal cell infuscated ; second submarginal cell rather short, its proximal end not quite reaching the 

 proximal end of the second posterior cell ; the usual stump of a vein rudimentary or wanting. 



Length, including the forceps, 15-19 millim. 



Female. Like the male, except the abdomen : segments 2-6 dull grey above and below, with dull black dorsal 

 spots, leaving a broad, ill-defined grey margin posteriorly and on the sides (the posterior margin 

 occupies somewhat less than one half of the segment). Ovipositor comparatively short, equal in length to 

 about three of the preceding segments united. The wings without costal expansion ; stump distinct. 



Length, without ovipositor, 13-17 millim. 



Hab. Mexico, Northern Sonora (Morrison). 



I have about forty males and thirty females, collected by the late Mr. Morrison. 



In E.prolificus, as in many other species, the cephalic and thoracic macrochsetee often 

 vary from black to yellowish ; sometimes the mystax contains many yellow bristles, some- 

 times not. In some rare specimens the tuft of white hairs in front of the scutellum is 

 wanting. 



This species seems to be a very common one, judging from the number of specimens col- 

 lected, and yet I cannot identify it with any description. In E. jubatus, Willist. (Trans. 

 Am. Ent. Soc. xii. p. 66), from New Mexico, judging from the description, there is no 

 white hair either on or in front of the scutellum j the abdominal segments 3, 4, 5 (and 

 not 2, 3, 4) have grey margins, and the segments 6 and 7 (and not 5, 6, 7) are silvery ;■ and 

 the abdomen of the female is deep black, which is not the case in E. prolijicus &c. 



E. parvulus, Bellardi, from Mexico, has reddish rings at the tip of the femora. 



E. nigrimystaceus, Macq. Dipt. Exot. Suppl. ii. p. 41 (Guadeloupe), has some points 

 in common with E. prolificus, but cannot be identified with it. 



N.B.— The species Nos. 8-11, as well as E. unicolor, Bell., E. jparvulus, Bell., 

 E. carinatus, Bell., and E. comatus, Bell., belong to a group which seems to be abun- 

 dantly represented in Mexico and in the neighbouring regions of the United States. 

 The species of this group have a crest of erect hairs along the middle of the thorax, the 

 crest usually ending posteriorly in a tuft of white or yellowish hairs inserted on the prse- 

 scutellar region and on the disc of the scutellum. The thorax itself is compressed from 

 the sides, with a kind of keel or ridge along the dorso-central line upon which the crest 

 is inserted: this character is more pronounced in some species than in others, and 

 amongst those now before me it is most distinct in Erax No. 9. In the male the costa 

 is expanded and thickened. A secondary sexual character in this group consists in the 



2d2 



