The following paper deals with six apparently undescribed species of Hercostomus collected from localities in the western United States and Canada.
Hercostomus chaetilamellus n. sp.
Male. Length, 4 mm.; of wing, 3.8 mm. Face wide, silvery white. Front silvery white, concolorous with face. Antennae black, the third joint about as long as broad, evenly rounded below. Orbital cilia white, the uppermost bristle black. Palpi and proboscis yellow.