Pachylyroceras is a large, generally subglobular, Upper Mississippian gonitite and included in the cephalopod subclass Ammonoidea.
Its suture has a narrow bifurcated ventral lobe with slightly divergent to subparallel sides and a median saddle less than half the height.
Pachylyroceras, named by Ruzhentsev & Bogoslovskaia (1971), is included in the Neoglyphiocerataceae, (sometimes written Neoglyphioceratoidea), but its position within the superfamily varies according to whose classification.
The revised version of the Treatise, Part L (W. M. Furnish et al. 2009 ) includes Pachylyroceras as well as Alaoceras, Caenolyroceras, Dombarigloria, and Lyrogoniatites in the Neoglyphioceratidae and subfamily Lyrogoniatitinae.
The Treatise (Miller, Furnish, and Schindewolf 1957) includes Lyrogoniatites, from which Pachylroceras is probably derived, in the subfamily Neoglyphioceratinae along with Neoglyphioceras, but in the superfamily Goniatitaceae.