A new heterostracan from the upper silurian of Northwest Territories, Canada

The new genus and species Alainaspis platyrhina from the Silurian of Prince of Wales and Somerset Islands, Northwest Territories, Canada is a large cyathaspidid of the subfamily Poraspidinae with distinctive proportions of probable adaptive significance. It is most closely related to Boothiaspis, previously described as an amphiaspid, but here reassigned to the Poraspidinae. The distribution of this genus helps to provide local correlation between the lower member of the Peel Sound Formation and the Somerset Island Formation on Prince of Wales and Somerset Islands. Associated invertebrates and vertebrates indicate a late Ludlovian to Pridolian age for the fauna.