Labra and faces. a, Labrum of Heriades apriculus Griswold, female (Megachilidae); b, Labrum of Anthophora edwardsii Cresson, male (Apidae); c, Face of Andrena mimetica Cockerell, female (Andrenidae); d, Face of Halictus farinosus Smith, female (Halictidae). (The heavy lines across the tops of a and b represent diagrammatically the clypeal articulations. b, c, from Michener 1944. (source: Michener, 2007)