16 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.52. 



The head seen from in front is broader than long and almost as 

 broad as the thorax. The compound eyes are large and strongly 

 arched. The inner margins are divergent at the clypeus, rarely sub- 

 parallel, and the lower margin reaches the base of the mandible. The 

 facets near the inner border of the eye are slightly larger than those 

 near the outer border, the change in size from one margin to the other 

 being almost imperceptible. The frons on the males is usually nar- 

 rower than the compound eye measured at the level just above the 

 insertion of the antennae ; on the females it equals or exceeds the width 

 of the eye at the same level. The ocellar cicatrices are flat, not sunk 

 in a pit, and are semicircular in form. The anterior one is greater 

 than a semicircle, somewhat horseshoe-shaped, with the opening 

 directed toward the clypeus; the posterior ones are a trifle greater 

 than a semicircle, of which the open side is toward the compound 

 eye. The precipitous posterior surface of the head is concave and the 

 temples are quite narrow. 



The outer border of the mandible is entire, the apex simple, and 

 the inner border provided with three teeth. The labrum is relatively 

 flat, longer than broad, and, as in the case of Bicyrtes, is bluntly 

 rounded at the end, not emarginate. The maxillae are moderately 

 long, stoutly developed and each is half -conical in form so that when 

 the two are approximated they form a tube within which lies the 

 tongue. The maxillary palpi consist of six segments, the labial of 

 four. As in the case of Bembix the maxillae when folded at rest are 

 concealed beneath the labrum. The clypeus is wider than long and is 

 but slightly arched, less so than in the case of Bembix. On the distal 

 median part above the base of the labrum there is in nearly all species 

 a somewhat triangular area above which on the median line there is 

 a short but evident carina continuous with the median carina of the 

 frons separating the antennas. On either side of this carina the 

 base of the clypeus slopes abruptly in toward the insertion of the 

 antenna. The antennae are inserted quite close to the base of the 

 clypeus and consist in the female of 12 segments, in the male of 13, 

 in which case several of the flagellar segments may bear modifications 

 that are useful in determining species. 



As in the case of Bembix the dorsum of the thorax is relatively flat, 

 the posterior border of the prothorax is much below the level of the 

 scutum, and the tubercles do not reach the tegulae. The suture be- 

 tween the sternum and episternum of the mesothorax is obliterated. 

 The median segment shows a clearly denned, broad, dorsal middle- 

 field, which is continued upon the almost vertical posterior surface 

 of the segment. The lateral angles of the segment are roundly 

 prominent, not so sharply compressed as in the case of Bicyrtes 

 nor so bluntly rounded off as in the case of Bembix. 



