Abstract
A study of pyritic and three‐dimensional specimens of sinograptids from the early Middle Ordovician Ningkuo Formation of western Zhejiang Province, south‐east China, indicates that the proximal development of both TylograptusSinograptus is of modified isograptid type. The thecal apertures of the two genera are reconstructed and display a complex morphology more typical of stratigraphically younger graptoloids. Because of differences in its prothecal folds and thecal apertures Tylograptus is distinguished from Holmograptus and regarded as a valid genus. In Sinograptus, a tongue‐shaped structure, and constriction of the thecal tube after the metathecal fold, are illustrated for the first time. The proximal development and thecal structures of TylograptusSinograptus imply a possible origin of sinograptids from earlier didymograptids or sigmagraptids. Four species, Tylograptus intermediusT. globiformisSinograptus typicalisS. rastritoides, are revised.
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