The Silurian graptolite genera Streptograptus and Pseudostreptograptus

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 longitudinal convexity to the platform and bear lateral spines/spatulate processes. Isolated material of 12 species, mostly from Osmundsberget, Sweden, is described.