"While often distinctly metallic blue to green (Fig. 2), duller forms (Fig. 1) may be confused with the more robust-bodied P. pubescens (LeConte). The elytral form of P. caeruleipennis is similar to that of P. pallipennis (Say) and P. affiliatus (Fall). The elytra are
elongate and feebly depressed in the apical third with the apices not being perceptibly tumid in caeruleipennis, contrary to the commonly expressed tumidity observed in pallipennis and affiliatus, which have variable elytral patterns often with four pale maculae, but never metallic or green-blue monochromatic." (from Leavengood 2014)