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The type species of the Ordovician agnostid trilobiteGeragnostus Howell, 1935

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Kurzfassung

Die Typus-Art des im Ordoviz weitverbreiteten agnostiden TrilobitenGeragnostus, G. sidenbladhi (Linnarsson, 1869) aus dem Ceratopygekalk des oberen Tremadoc von Schweden, wurde erneut untersucht und ein Lectotypus festgelegt.Geragnostus Howell, 1935, besitzt eine große Ähnlichkeit mitArthrorhachis Hawle & Corda, 1847. Beide Gattungen sind offensichtlich nah verwandt, undGeragnostus wird sich eventuell als jüngeres subjektives Synonym vonArthrorhachis herausstellen. Eine Trennung vonGeragnostus undArthrorhachis könnte aufrechterhalten werden, wenn man zuArthrorhachis metagnostide Trilobiten rechnet, in denen der hintere Lobus (M3) der Pygidium-Spindel deutlich kürzer ist als die Länge (sag.) des vorderen und mittleren Lobus zusammen (M1 + M2).

Abstract

The type of the widespread Ordovician agnostid trilobiteGeragnostus, G. sidenbladhi (Linnarsson, 1869) from the upper Tremadocian Ceratopyge Limestone of Sweden, is redescribed and a lectotype is selected.Geragnostus Howell, 1935 bears a strong similarity toArthrorhachis Hawle & Corda, 1847. Obviously the two genera are closely allied, andGeragnostus may eventually be regarded as a junior subjective synonym ofArthrorhachis. It is suggested, however, that the distinction betweenGeragnostus andArthrorhachis might be upheld if the latter genus is taken to include metagnostids in which the posterior lobe (M3) of the pygidial rhachis is distinctly shorter than the length (sag.) of the anterior and middle lobes combined (M1 + M2).

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  1. Department of Historical Geology and Palaeontology, Sölvegatan 13, S-223 62, Lund, Sweden

    Per Ahlberg

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Ahlberg, P. The type species of the Ordovician agnostid trilobiteGeragnostus Howell, 1935. Paläont. Z. 63, 309–317 (1989). https://doi.org/10.1007/BF02989517

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