A new agnathan from the Lower Devonian of Arctic Canada, and a review of the tessellated heterostracans

A new tessellated heterostracan, Aporemaspis pholidata gen. et sp. nov., is described from the Snowblind Bay Formation of Cornwallis Island in the Canadian Arctic Archipelago. Its age is late Lochkovian, and it is thought to be related to other tessellated forms from the Delorme Formation, District of Mackenzie, NWT. Two fragments of armour from the Delorme Formation are tentatively assigned to Aporemaspis gen. nov. The known genera of tessellated heterostracans are reviewed, and it is concluded that at present our knowledge of the group is insufficient to support a meaningful classification, although it is clear that the Ordovician genera should not be considered to be heterostracans. -Authors