Twenty six of the more important species of monograptids (s.l.), retiolitids and Cyrtograptus (from a total fauna of 52 species) are described from Wenlock strata of the Cape Phillips Formation, Canadian Arctic Archipelago. Of this fauna, eight new species or subspecies, Monograptus firmus festinolatus, M. instrenuus, M. opimus, M. testis incomptus, Cyrtograptus falcatus, C. hamatus brevis, C. kolobus and C. pseudomancki, are described and illustrated.Wenlock biostratigraphic zones comprise the Cyrtograptus centrifugus-C. insectus Zone (earliest Wenlock), M. instrenuus-C. kolobus Zone, tentatively divisible into lower and upper subzones, C. perneri-M. opimus Zone possibly divisible into lower and upper subzones, C. lundgreni-M. testis Zone divisible into a lower M. testis incomptus Subzone and an upper M. testis testis Subzone, and the Pristiograptus ludensis Zone (latest Wenlock).

Llandoverian graptolite faunas from 13 major sections in a region extending from the southern Northwest Territories to northern Yukon are divisible into 13 zones, oi v^\\\c\\{\\q persculptus and magnus zones are only tentatively recognized. The biostratigraphic units, from oldest to youngest, are the persculptus Zone?, acuminatus Zone, atavus Zone, acinaces Zone, gregarius Zone, triangulatus Zone, magnus Zone?, argenteus Zone, convolutus Zone, sedgwicki Zone, turriculatus Zone, spiralis Zone, and sakmaricus-laqueus Zone. This study describes 101 species of graptolites. The number of species described for each genus is as follows: nine species of Petalograptus , three of Cephalograptus , two of Rhaphidograptus , three of Dimorphograptus , two of Retiolites, three of Stomatograptus , four of Pseudoplegmatograptus , two of Lagarograptus , two of Atavograptus, four of Coronograptus, ihrQQ of Pribylograptus, three of Pristiograptus , one of Monoclimac is , 46 of Monograptus , 12 of Rastrites , and one each of IDiversograptus and Barrandeograptus. One new species, Rastrites rostratus, and one new subspecies, Monograptus runcinatus richardsonensis, are described.

Geochemical data from the Cape Phillips Formation, Arctic Canada, are examined in association with three Silurian biotic crises in the graptolite community; the early Wenlockian Ireviken, mid Wenlockian Cyrtograptus lundgreni, and end Wenlockian Colonograptus ludensis extinction events. Positive δ13Corg excursions are associated with the Ireviken and C. lundgreni events, but not the Co. ludensis Event. The Ireviken and C. lundgreni excursions are recognized worldwide and are herein interpreted to be the result of carbonate weathering in response to eustatic sea-level drop. The C. lundgreni excursion is of greater magnitude in the more proximal basin margin section at Abbott River, Cornwallis Island, and is explained by the amplification of a more strongly positive δ13C signature in shallower parts of an epeiric basin during increased exposure and weathering of the carbonate shelf. Excursion C5, within the C. praedeubeli – C. deubeli Zone, is also of regional significance, as it occurs in both the Abbott River section and Twilight Creek section on Bathurst Island, and is also recognized in Estonia, Poland, and England. Excursion C6 is recognized in the Gorstian Stage, yet its regional significance remains equivocal. There is a reasonable general agreement between the shape of the δ13Corg and δ13Ccarb curves, yet the δ13Ccarb curve is largely a record of detrital carbonate derived from the shelf. The δ13Corg curve represents extraction of dissolved inorganic carbon by plankton and thus is more indicative of ambient paleoceanographic conditions. These data are valuable in that they provide a detailed secular marine δ13C curve for the Wenlockian of Arctic Canada from relatively unaltered sections of varying facies whose ages are well constrained by graptolite biostratigraphy.

A cladistic, phylogenetic analysis of the Retiolitidae, using 18 genera and parataxa and 23 characters, reveals that two distinct clades can be recognized within this family, as well as a primitive stem‐group that includes the genus Pseudoretiolites. One of the derived clades includes Pseudo‐plegmatograptus, Stomatograptus and Retiolites, which are assigned to the revised subfamily Retiolitinae. The other derived clade, the early part of which shows a paraphyletic relationship, includes the remaining known genera Rotaretiofites s.l., Paraplectograptus s.l., Sokolovograptus, Plectograptus, Agastograptus, Spinograptus, Gothograptus, Eisenackograptus, Neogothograptus, Semiplectograptus, Plectodinemagraptus and Holoretiolites. These genera are all included within an expanded Plectograptinae. The biostratigraphic distribution of these taxa suggests that these two clades diverged from a Pseudoretiolites‐like ancestor in mid‐Aeronian time.

Integration of graptolite data obtained from isolated and flattened material from Arctic Canada permits the recognition of three upper Homerian biostratigraphic zones. These, from oldest to youngest, are the Pristiograptus dubius – Gothograptus "nassa" interval Biozone, Colonograptus? praedeubeli – Colonograptus? deubeli Biozone, and Colonograptus? ludensis Biozone. Species of flattened graptolites described in this study include C.? deubeli, C.? ludensis, C.? praedeubeli, Colonograptus? schedidoneus,Lobograptus ? angustus n.sp., Lobograptus? claudiae, Lobograptus? sherrardae, Plectograptus macilentus, Agastograptus clathrospinosus, and Gothograptus "nassa." With only a few exceptions, the zone-by-zone diversity of monograptid and plectograptine graptolites of the Canadian Arctic is remarkably similar to that elsewhere.

The Canadian Arctic Islands Wenlock is represented by a diverse assemblage of graptolites from the Cape Phillips Formation. Cyrtograptids are continuously present throughout all but the uppermost Wenlock. Species of Cyrtograptus constitute the main basis for biostratigraphic zonation, supported to a much lesser degree by Monograptus, Monoclimacis, and Pristiograptus through most of the series. The uppermost Wenlock is dominated by Pristiograptus in association with rare Gothograptus.The following biostratigraphic zones and their correlations are proposed: (1) Cyrtograptus centrifugus – Cyrtograptus insectus Zone (earliest Wenlock); (2) Cyrtograptus aff. rigidus – Monograptus aff. riccartonensis Zone (late early Wenlock); (3) Cyrtograptus perneri – Monograptus cf. munchi Zone, in which Cyrtograptus multiramis is a particularly common element (mid-Wenlock age); (4) Cyrtograptus lundgreni – Monograptus testis Zone, divisible into a lower Monograptus testis n.ssp. and an upper Monograptus testis testis Subzone (late Wenlock); and (5) Pristiograptus ludensis Zone (latest Wenlock). The second and third zones are also possibly divisible into lower and upper subzones, but with less certainty.The degree of zonal subdivision in the Cape Phillips is lower than in Europe. It was observed locally that a number of the key species showed a high degree of overlap and some inconsistencies in their ranges from section to section.Paleoecologically, a few species, particularly Cyrtograptus preclarus, Cyrtograptus cf. malgusaricus, and Pristiograptus meneghini, appear to have preferred basin-margin regions.

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Twenty-two graptolite species are described from the Tremadoc portion of the Road River Group. In a 220 m thick, graptolite-rich section on Peel River, six graptolite biozones are recognized which in ascending order are: Staurograptus dichotomus, Anisograptus matanensis, Adelograptus cf. A. tenellus, Adelograptus antiquus, Kiaerograptus pritchardi and Paradelograptus kinnegraptoides. The Psigraptus fauna appears to be confined to a single bedding-plane within a thick interval dominated by Adelograptus cf. A. tenellus, and for this reason we propose a new zone characterized by the latter species rather than identify a Psigraptus Biozone as in China. The Adelograptus cf. A. tenellus Biozone has yielded Adelograptus? bulmani Spjeldnaes 1963, which we propose as the type species for the new genus Ancoragraptus. Graptolites recorded from the Tremadoc of the Yukon for the first time are: Ancoragraptus bulmani, Clonograptus magnificus, C. cf. C. multiplex, C. cf. C. rigidus, Hunnegraptus copiosus, Kiaerograptus? bulmani and K? kutchini sp. nov.