Silurian retiolitids from the Cape Phillips Formation, Arctic Islands, Canada

Isolated retiolitids recovered from limestone concretions in the Cape Phillips Formation include Pseudoplegmatograptus obesus obesus, Pseudoretiolites cf. decurtatus, Retiolites geinitzianus densireticulatus, Stomatograptus grandis grandis, S. grandis imperfectus, S. sp., Paraplectograptus eiseli, P. praemacilentus, P. sp. A, Plectograptus (Sokolovograptus) textor, Gothograptus eisenacki and Holoretiolites simplex. Plectograptits! textor is assigned to Plectograptus (Sokolovograptus), the definition of Paraplectograptus is expanded to include morphs with a weak reticulum, and we show that reticular development and density is highly variable within these genera. Retiolites may occasionally retain a partially to well developed prosicula; Stomatograptus and Pseudoplegmatograptus have a consistently well developed prosicula; and Pseudoretiolites possesses a well developed prosicula and, rarely, a metasicula. A sicula has not been seen in either Plectograptus (Sokolovograptus) or Paraplectograptus. Surface sculpture is consistent within the subfamilies Retiolitinae and Plectograptinae, and serves to distinguish them. Age ranges of taxa recovered in this study are as follows. Pseudoretiolites: triangulatuslmagnus to turriculatus zones; Pseudoplegmatograptus: turriculatus Zone; Stomatograptus spp.: spiralis to testis zones; Retiolites densireticulatus: spiralis to testis zones; Plectograptus (Sokolovograptus) textor: turriculatus to nassa zones', Paraplectograptus spp.: turriculatus to nassa zones; Gothograptus eisenacki: nassa Zone; Holoretiolites: nilssoni Zone.