The lower facial margin is sometimes called the epistoma, but this term should be avoided because it is ambiguous (Crampton 1942, pp. 16-17).
Reference:
Crampton, G.C., 1942. A guide to the insects of Connecticut. Part VI. THe Diptera or true flies of Connecticut. First Fassicle. The external morphology of the Diptera. - Bulletin of the Connecticut State Beological and Natiral History Survey 64: 10-165. (Reprint 1966).
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