For full-size image click here.

In his description of C. pallidipenne, Townes(1) stated:

"clypeus in front view with the apex strongly and broadly arcuately concave; mandible (when not eroded) about 0.75 as long as the clypeus is wide, its apical tooth moderately broad."
I've added double arrows to this crop of the 4th image in the series, to indicate my interpretation of the characterization Townes gave regarding the measurements for the mandible length vis-a-vis the clypeus width.

The blue double arrow indicates the width of the clypeus...it measures ≈454 pixels (using the Photoshop measuring tool on the image).

The green double arrow indicates the (somewhat fore-shortened) length of the mandible, from base to tip...it measures ≈330 pixels.

That gives a ratio of 330/454 ≈ 0.73, which is reasonably close to the value of 0.75 given by Townes for C. pallidipenne, especially if one considers that the fore-shortening of the mandible in the perspective here will tend to give an underestimate for its length, and thus reduce the ratio.