Journal of Systematic Palaeontology 2 (2): 65–93 Issued 23 July 2004 DOI: 10.1017/S1477201904001117 Printed in the United Kingdom C  The Natural History Museum The Silurian Graptolite genera STREPTOGRAPTUS and PSEUDOSTREPTOGRAPTUS David K. Loydell School of Earth and Environmental Sciences, University of Portsmouth, Burnaby Road, Portsmouth PO1 3QL, UK J¨ org Maletz Department of Geology, State University of New York at Buffalo, 772 Natural Sciences and Mathematics Complex, Buffalo, New York 17260-3050, USA SYNOPSIS Streptograptus is a common, diverse and stratigraphically important Telychian graptolite genus. It is characterised by the presence of a centrally-placed nozzle in the metatheca. Five species groups of Streptograptus are recognised, based upon the presence or absence of thecal characters, the most important of which are (all terms are new): cupulae, which are protuberances at the base of the theca; the platform, a concave depression with a central longitudinal convexity in which the metatheca sits; the distal lobes, extensions of the dorsal metathecal wall; and the apron, secondary fusellar growth over the original metatheca. Pseudostreptograptus thecae lack the central longit- udinal convexity to the platform and bear lateral spines/spatulate processes. Isolated material of 12 species, mostly from Osmundsberget, Sweden, is described. Cupulae, the platform and ventral rhabdosome curvature appeared at the beginning of the Telychian, the apron at the beginning of the turriculatus Zone. In the subsequent crispus and sar- torius zones some new character combinations arose (platforms in proximal thecae only of S. crispus, a species that lacks cupulae), whilst others reached their greatest recorded level of development (central longitudinal convexity and marginal flanges to platform in S. loydelli, apron in S. sartorius). KEY WORDS Llandovery, Sweden, Osmundsberget, Telychian, graptoloid E-mail: David.Loydell@port.ac.uk. E-mail: jorgm@acsu.buffalo.edu. Contents Introduction 66 Material and methods 66 The Osmundsberget section 66 The Solberga section 68 Characters 68 Sicula 68 Origin of theca 1 68 Cupulae (singular cupula: new term) 68 Prothecae 69 Platform (new term) and rim/flange 69 Nozzle 69 Distal lobes (new term) 69 Apron (new term) 69 Thecal spines 69 Interthecal septa 69 Rhabdosome shape 69 Species groups 70 Group 1 70 Group 2 70 Group 3 70 Group 4 70 Group 5 70 Pseudostreptograptus 70