The palaeostomatopod crustaceanBairdops beargulchensis Schram & Horner, 1978 (Malacostraca, Hoplocarida) from the Mississippian Bear Gulch Limestone is now seen as a taxonomic composite that arose from the confusion of specimens of two distinct hoplocarid species. These species are herein described as the palaeostomatopodBairdops beargulchensis Schram & Horner, 1978 and a new species of archaeostomatopod, Tyrannophontes acanthocercus.Tyrannophontes acanthocercus is quite distinct from the Pennsylvanian archaeostomatopodT. Theridion from the Essex fauna (Mazon Creek), with which it was originally compared.Bairdops beargulchensis is very similar to the Mississippian palaeostomatopod,B. elegans, from the Scottish Glencartholm fauna. A previously proposed synonymy ofB. beargulchensis withT. theridion is therefore rejected. A preliminary restudy of the archaeostomatopodsT. Theridion andGorgonophontes peleron, and the palaeostomatopodsPerimecturus Rapax andP. parki, reveals some newly recognized characters of those taxa and suggests some novel interpretations of hoplocarid evolution. A cladistic phylogenetic analysis of the Hoplocarida including the Paleozoic forms resolves the higher level relationships of the hoplocarids (palaeostomatopods, archaeostomatopods, aeschronectids, and unipeltatans).

The palaeostomatopod crustaceanBairdops beargulchensis Schram & Horner, 1978 (Malacostraca, Hoplocarida) from the Mississippian Bear Gulch Limestone is now seen as a taxonomic composite that arose from the confusion of specimens of two distinct hoplocarid species. These species are herein described as the palaeostomatopodBairdops beargulchensis Schram & Horner, 1978 and a new species of archaeostomatopod, Tyrannophontes acanthocercus.Tyrannophontes acanthocercus is quite distinct from the Pennsylvanian archaeostomatopodT. Theridion from the Essex fauna (Mazon Creek), with which it was originally compared.Bairdops beargulchensis is very similar to the Mississippian palaeostomatopod,B. elegans, from the Scottish Glencartholm fauna. A previously proposed synonymy ofB. beargulchensis withT. theridion is therefore rejected. A preliminary restudy of the archaeostomatopodsT. Theridion andGorgonophontes peleron, and the palaeostomatopodsPerimecturus Rapax andP. parki, reveals some newly recognized characters of those taxa and suggests some novel interpretations of hoplocarid evolution. A cladistic phylogenetic analysis of the Hoplocarida including the Paleozoic forms resolves the higher level relationships of the hoplocarids (palaeostomatopods, archaeostomatopods, aeschronectids, and unipeltatans).