(Fig. 39–47)
Hydrosmecta pseudodiosica Lohse, in Lohse et al. 1990: 149. Majka and Klimaszewski 2008; Webster et al. 2012.
Diagnosis. Body length 2.5–2.7 mm; body brown to piceous, dull, elytra and legs dark brown (Fig. 39); microsculpture of forebody minute, consisting of rounded meshes; head subquadrate, at eye level about as wide as at level of tempora; eyes about as long as postocular region in dorsal view; antennae slender, antennomeres II and III subequal in length, following ones elongate but decreasing in length toward apex; glossa thin and long, Y-shaped, deeply split apically; each mandible with subapical tooth; pronotum transverse, 1.25 as broad as long and 1/6 broader than head, broadest near apex, sides converging basally to obtuse posterior angles; elytra at suture 1.3 as long as pronotum along midline of disc, about 1.2 as broad as pronotum; abdomen subparallel, tergites becoming longer toward apex. Male: tergite VIII broadly arcuate (Fig. 42); sternite VIII with apical margin straight medially, very broadly rounded laterally (Fig. 43); median lobe of aedeagus with narrowly oval bulbus, evenly coalescent with short triangular tubus in dorsal view (Fig. 41); in lateral view tubus with apical part narrow, directed slightly ventrad (Fig. 40); internal sac with two elongate structures in bulbus (Fig. 41). Female: tergite VIII truncate apically (Fig. 44); sternite VIII with apical margin moderately produced, with moderately deep, rounded emargination at middle (Fig. 45); spermatheca with capsule small, spherical, with shallow and moderately wide apical invagination, stem long, irregularly twisted and swollen posteriorly (Fig. 46, 47).
This species is similar to H. odiosica Casey from California, but has a larger and longer body (H. odiosica is 1.8 mm long) and a more transverse pronotum.
Distribution. Origin: Nearctic. Canada: NB, ON, YT. USA: not recorded.
Collection and habitat data. Habitat: riparian habitats, sandy and cobblestone shores of brooks and rivers; adults under small cobblestones and gravel set in sand on a partially shaded cobblestone bar near the outflow of a brook into a clear rocky river. Collecting period: V, VI. Collecting method: hand collecting or aspirating specimens from near and under cobblestones at edges of streams.