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

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Abstract
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. Plectograptus? 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 Pseudoretio/ites 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: triangulatus/magnus to turri­culatus zones; Pseudoplegmatograptus: turriculatus Zone; Stomatograptus spp.: spiralis to testis zones; Re­tiolites densireticulatus: spiralis to testis zones; Plectograptus (Sokolovograptus) textor: turriculatus to nassa wnes; Paraplectograptus spp.: tulliculatus to nassa zones; Gothograptus eisenacki: nassa Zone; Holoretio­lites: nilssoni Zone.

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