4 PROCEEDINGS OF THE NATIONAL MUSEUM vol.71 



Behind this comes the remainder of the abdominal mass (the body 

 behind the slender portion of the petiole is, for convenience, called the 

 abdomen in this paper) having the usual characters. The surface is 

 smooth or, at most, only minutely sericeous, except in the male of 

 one species (argentifrons) , and with a few rather short, scattered erect 

 hairs. Above, these are almost or entirely on the terminal plate. 

 Below, they are most numerous on the terminal plate, but a few may 

 be present on the more anterior sterna. The form of the tip differs 

 according to the sex (see Sex Distinctions) . The posterior outline of 

 the last ventral abdominal plate varies somewhat in different species, 

 but this is, unfortunately, also the case in examples of the same spe- 

 cies, which prevents use of this feature as a trustworthy distinction 

 for species. 



The wings show little difference from those of related groups. The 

 tegula is generally smooth and glistening. The larger wing veins are 

 generally darker than the smaller ones and usually dark brown or 

 piceous. The wing surface varies from hyaline, through various 

 stages of darkening, to fuliginous, which is accompanied by a deep 

 blue or violet reflection. The depth of this darkening is usually 

 greatest toward the tip of the wing beyond the ends of the veins and 

 cells. 



The veins and cells themselves vary greatly, particularly the radial 

 and second and third cubital cells. The radial cell may be rather 

 long for its width, or short and broader; the transverse cubital veins 

 may vary somewhat in their distance apart and in the paths they 

 follow, resulting in differently proportioned cubital cells, particularly 

 the third cubital. Modification of vein arrangement, the introduc- 

 tion or omission, partial or entire, of veins often occurs, giving nu- 

 merous abnormalities such as a petiolated second cubital cell, etc. 

 Though such variations are usually present on both pairs of wings, 

 this is not always the case, as examples with a petiolated second cub- 

 ital cell on one side and normal conditions on the other, occur. In 

 general, variations in venation are most frequently found in examples 

 which are below normal size for a species, in small species, and in 

 males. 



The legs in this genus, as in all Sphecidae, are rather long. The 

 coxae, trochanters, and femora may bear hairs, usually decreasing in 

 number passing outward along these segments, and some face or 

 faces of them may be more or less sericeous. Spines appear on the 

 tibiae and tarsi, not very long on the tibiae but quite stout. On the 

 tarsi they are usually longer, as compared with the length of the seg- 

 ment, than on the tibiae. The cleaning spine at the tip of the hind- 

 tibia has the teeth on the outer half of the spine at least, coarser and 

 more separated than in the genus Sjphex. In the females the spines 

 on the outer side of the fore metatarsus are usually seven in number, 



