The writer (Dell, 1964a: 226) included Pholadomya mawsoni Hedley in the synonymy of arcaeformis and subsequently (Dell, 1972b: 27) included Lyonsiella planulala Thiele under the same name. Comparison of type material and topotypes, and the examination of much additional material bears out this action and confirms the generic placing in Lyonsia. L. arcaeformis is the only representative of Lyonsia in antarctic waters, although three species, alvarezi Orbigny, 1846, malvinensis Orbigny, 1846, and fretalis Dall, 1915, have been described from off southern South America. Of these, fretalis is the closest to arcaeformis.

Lyonsia arcaeformis would appear to have a circumantarctic distribution, having been recorded from 53°E to the Ross Sea and also the Antarctic Peninsula, the South Shetlands, South Orkneys, and South Georgia in depths from 12-1771 m. Within the Ross Sea it is known from depths of 328-475 m.