The following new Toernquistiidae from Whiterockian (Llanvirn to lower Caradoc) strata of the Precordillera, western Argentina, are described: Chomatopyge canasi new species, Lasarchopyge benedettoi new genus and species, Lasarchopyge correae new genus and species, Lasarchopyge new species A, and Paratoernquistia sanchezae new genus and species. Phylogenetic analysis suggests that the Toernquistiidae Hupe, 1953 (including Chomatopyge, Lasarchopyge, Mesotaphraspis, Paratoernquistia, and Toernquistia) is closely related to but distinct from the Dimeropygidae Hupe, 1953 (including Ischyrotoma, Ischyrophyma and Dimeropyge). It is difficult to find unique synapomorphies that unite toernquistiids and dimeropygids into a monophyletic group that excludes other proetides (e.g., hystricurids), although details of their ontogenies are similar. Several species of Toernquistiidae are known from the Argentine Precordillera (one species previously described), and other species of this family have been described from Australia, Baltica, China, Kazakhstan and Laurentia. Members of the Dimeropygidae are known only from Baltica and Laurentia.

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