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Medium-sized (11.7-14.0mm); body moderately broad and dark brown or dull black; pronotum with coarse, sparse puntures; elytra finely and densely pitted; elytral striae completely and faintly impressed; coarsely punctate; elytron flattened medially with blunt but distint carina on 5th interval; area medial to carina elevated and flat; area lateral to carina slightly concave. (See also identification of genus).

Holometabolous. Amphizoids lack structural adaptations for swimming, and are actually more efficient locomotors on land than in water. The beetles are unable to swim, and crawl on substrate at the bottom of streams. Larvae pupate out of the water on adjacent streambanks. Both adults and larvae are strict predators. Adult Amphizoids are able to carry out most life functions- feeding, locomotion, oviposition- as easily on land as in water. Under laboratory conditions, Amphizoid eggs and larvae thrive out of water, and even pupate normally. Larvae are of the caraboid type, and are elongated with flattened lateral lamellate projections, have two tarsal claws, and two short, spine-like cerci. Larvae breathe through the 8th abdominal segment. When disturbed, adults exude a yellowish fluid from the anus which has an odour described as that of cantaloupe melon or rotting wood. The function of this fluid is debated, but it is likely for predator-defense. Both adults and larve are frequently found attached to the roots of undercut vegetation at the stream edge, crawling along rocks and pebbles on the bottom of the stream, or found clinging to driftwood and other debris. When disturbed they can be seen floating on or near the water surface.

Extends from southern Yukon Territory, south along Rocky Mountains through Alberta and British Columbia to Chuska Mountains of northeast Arizona and the Sangre de Cristo range of northern New Mexico; eastward from Wallowa Mountains of northeastern Oregon and Independence Mountains of northeastern Nevada to the Bighorn Mountains of north-central Wyoming and the Front Range of central Colorado.