Article: Zosterogrammida, a new order of millipedes from the middle Silurian of Scotland and the upper Carboniferous of Euramerica

New Palaeozoic millipedes, Zosterogrammus stichostethus gen. et sp. nov. and Casiogrammus ichthyeros gen. and sp. nov., are described from the Francis Creek Shale Member of the Carbondale Formation (Upper Carboniferous: Pennsylvanian), Mazon Creek, Illinois, and the Hagshaw Hills Inlier (Middle Silurian: Wenlock) of the Midland Valley of Scotland, respectively. These millipedes, together with Purkynia lata Fritsch from the Upper Carboniferous (Westphalian D) of Nyrany, Czech Republic, are placed in the new family Zosterogrammidae within the new order Zosterogrammida. All of these millipedes have very broad terga with a microsculpture consisting of fine transverse terrace lines along the anterior of the terga and oblique terrace lines across the remainder. Zosterogrammida have a trunk-ring architecture consisting of an arched diplotergite, a pair of free ventral diplopleurites and a pair of free ventral sternites, indicating a relatively basal phylogenetic position within Chilognatha. Although the exact phylogenetic position is indeterminate, Zosterogrammus stichostethus has divided sternites, indicating a possible affinity with the Pentazonia. The Hagshaw Hills millipede contributes significantly to the high-rank diversity of Middle Silurian millipedes as all previously described taxa of this age belong to the Archipolypoda.