The structure and affinities of Lapworthograptus grayae (Lapworth, 1876)

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Abstract
Synopsis: The graptolite Lapworthograptus (formerly Cyrtograptus ) grayae is redescribed. Evidence for branching is reassessed: two specimens (one the type) show somewhat equivocal evidence for the development of secondary branching, and in both instances the secondary ‘cladia’ appear to come from the upper part of the protheca, rather than from the thecal aperture as is normal. The distal thecae are folded back on themselves, with everted apertures which face proximally to proximo-dorsally; they are unlike those of the other branched monograptid genera Cyrtograptus, Diversograptus, Sinodiversograptus or Barrandeograptus. They resemble rather those of the monograptid species singularis and knockensis, and these graptolites are here assigned to the genus Lapworthograptus Bouček and Přibyl, 1952 (type species L. grayae ). The genus Prochnygraptus Přibyl and Štorch, 1985 (type species P. singularis ) therefore becomes a junior synonym of Lapworthograptus. L. grayae, knockensis and singularis occupy a shorter, and younger stratigraphic interval than previously thought, the crenulata to spiralis Biozones of the upper Telychian. Thus derivation of these species from previously postulated upper Aeronian ancestors seems unlikely. Lapwortho-graptus may have a streptograptid origin or, alternatively, could have originated via a Monograptus crispus–Monograptus wimani lineage late in the Telychian; this is suggested by an indication that grayae has biform thecae, as some isolated proximal ends bearing enrolled thecae, associated with the type and other material, may belong to this species.

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