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Extracted from: Snelling R.R., (1983). The North American Species of the Bee Genus Lithurge (Hymenoptera: Megachilidae). Contributioun in Science, number 343, pp. 1-11. The Natural History of Los Angeles County, 1983
No authentic material of L. planifrons has been available for study; the species is based on a unique male, and the original description is broad enough that it can be applied to almost any North American Lithurge male. Were it not for the descriptivespecific epithet chosen by Friese, this would remain a species of questionable identity.
Three males from Chamela, Jalisco, Mexico, collected by S. H. Bullock, are, I believe, representatives of this species. More important than that they agree with the original description is that the face is flat. The supraclypeal area is not at all elevated above the level of the clypeus and does not, in its upper portion, slope toward the antennal sockets. The only other species with a flat supraclypeal area is L. listrota-, males of L. listrota possess a prominent erect tubercle on the labrum, lacking in L. planifrons. In addition, males of L. listrota have a conspicuous median impunctate line on the supraclypeal area.
Since the male of L. planifrons lacks an erect labral tubercle, it resembles males of both L. apicalis and L. echino-cacti. From both of these species, L. planifrons is separable by the flat supraclypeal area, which does not have a median impunctate line. Instead, the supraclypeal area is conspicu-ously more coarsely punctate in the middle than on either side; these coarse punctures are subcontiguous, and a similar central line of coarse punctures is present on the clypeus. The supraclypeal area of L. apicalis and L. echinocacti is distinctly convex between the clypeal base and the antennal sockets (often depressed in the center in L. apicalis), and the middle is distinctly shiny and impunctate (sometimes the entire supraclypeal area sparsely punctate in L. apicalis).
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