Allotrichoma (Allotrichoma) occidentale Mathis & Zatwarnicki 2012

This species is distinguished from congeners by the following combination of characters: Small to moderately small shore flies, body length 1.60–2.00 mm. Head: Medial facial carina above facial prominence shallow; labella broad, fleshy, shorter than mediproboscis; clypeus microtomentose, usually gray. Thorax: Presutural supra-alar seta present. Pleural area lacking stripes. Wing with costal vein ratio 0.27–0.28; M vein ratio 0.41–0.50. Legs blackish brown to black; midtibia bearing numerous, erect setae along dorsal surface. Abdomen: Male 5th sternal flap in lateral view (Fig. 43) narrow, elongate, slightly widened apically, bearing 5–6 apical setulae, some from short tubercles; 5th medial process in lateral view (Fig. 43) relatively narrow, very elongate, apex slightly widened, bearing 4–5 setulae along anteroapical surface. Male terminalia (Figs 39–42): Epandrium in posterior view (Fig. 39) ovately rounded on dorsal half; epandrium in lateral view (Fig. 40) with anterior and posterior margins sinuous, relatively wide dorsally; cercus in posterior view (Fig. 39) broadly pointed dorsally, gradually broadened ventrally then abruptly curved or arched laterally and ventrally as a slightly tapered, elongate, arched process that bears numerous moderately long setulae apically, apex shallowly sinuous; cercus in lateral view (Fig. 40) nearly straight, wider dorsally, ventral half nearly parallel sided, apex broadened and shallowly bifurcate, bearing moderately long setulae; surstyli (ventral extensions of epandrium) in posterior view as parallel, narrow processes that bear setulae on apical portion; surstylus in lateral view (Fig. 40) elongate, narrow, nearly parallel sided, apical portion bearing very short setulae anteriorly and apically, with a short, lacking an apical process; aedeagus in ventral view (Fig. 41) elongate, narrowly ovate, tapered apically, in lateral view (Fig. 42) elongate, somewhat lunate; phallapodeme in lateral view (Fig. 42) triangular, keel shorter than length, narrow, somewhat pointed; gonite in ventral view (Fig. 41) bar-like, slightly wider basally, apex with short, lateral process, apex bearing setula, in lateral view (Fig. 42) wide basally, gently but distinctly arched, tapered to apex, apex with rounded notch, producing a subapical, short, nipple-like process that bear a setula.

(Fig. 44) Nearctic: Canada (Manitoba, Saskatchewan), United States (Alaska, Arizona, California, Idaho, Michigan, Montana, Nebraska, Nevada, North Dakota, Oregon, South Dakota, Utah, Washington, Wyoming).