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For larger, full-size image, click here
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Wing Venation Labels:

  Cells:   M = marginal cell;   S1 = 1st submarginal cell;   S2 = 2nd submarginal cell;   S3 = 3rd submarginal cell.
  Veins:   1m-cu = 1st recurrent (or medio-cubital) vein;   2m-cu = 2nd recurrent (or medio-cubital) vein;   r = radius.
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In terms of wing venation, the relative position of where the 1st recurrent vein (1m-cu) meets the 2nd submarginal cell (S2)...indicated in the image above by the pink arrow...is diagnostic in separating various pepsine genera. In particular, the situation for Pepsis, Hemipepsis, and Entypus is described below. Note that these three genera contain the largest sized individuals among all nearctic Pepsinae. According to Townes(1)(1957), the range of fore wing lengths in these genera are: Pepsis, 13—48mm ; Hemipepsis, 11—27mm; and Entypus, 9—26mm. The fore wing lengths for all other pepsine genera are given as less than or equal to 18mm in Townes(1).

The green and blue arrows in the image above (click here for larger image) point to the proximal and distal ends, respectively, of the posterior edge of the 2nd submarginal cell (S2). The pink arrow indicates the position of where the 1st recurrent vein (1m-cu) meets the 2nd submarginal cell (S2) along its posterior edge, and is a useful character for separating Pepsis, Hemipepsis, and Entypus:

In Pepsis, the 1st recurrent vein (1m-cu) meets the 2nd submarginal cell (S2) about 1/3 of the length of its posterior edge (or less) out from its proximal end;
In Entypus, the 1st recurrent vein (1m-cu) meets the 2nd submarginal cell (S2) near a point about 1/4 of the length of its posterior edge before its distal end;
In Hemipepsis, the 1st recurrent vein (1m-cu) meets the 2nd submarginal cell (S2) within 1/10 the length of its posterior edge from its distal end
By the above criteria, this photo above would best fall under Entypus, as the pink arrow is about 0.2 the distance away from the distal end of the posterior edge of S2.

It's also good to keep in mind that Pepsis can be separated from all the other genera in Pepsinae by its apically rounded marginal cell, in which the apical end of the bounding radius vein (r) "bends backwards" to meet the wing margin in an acute angle. Thus, this can immediately be seen to not be Pepsis...as the radius (r) meets the wing margin at a right angle.