A Late Middle Cambrian damesellid trilobite cranidium from Beaconsfield, Tasmania

Abstract

A recent discovery confirms the presence of damesellid trilobites in a late Middle Cambrian fauna from near Beaconsfield. Jago (1980)illustrated and briefly discussed a poorly-preserved late Middle Cambrian fauna from near Beaconsfield, which was discovered by Green (1959). In February 1980, Professor d.Green, Dr M.R. Banks and a party of geology students from the University­ of Tasmania collected further fossils from this locality. The fossils include the best preserved specimen (Plate 1, figs. 1 and 2)so far found at this locality. It is a substantially completle trilobite cranidium of a member of the Damesellidae; both the in­ ternal and external moulds are available. Of the specimens figured in Jago (1980) the cranidium figured in pl.1, fig. 17 and the pygidium figured in pl.1, fig. 21 probably belong in the same species as the newly discovered cranidium. As far as can be deter­mined, the Beaconsfield specimens probably belong in a new genus of the Damesellidae, which is characterized by a substantial spine emerging from the posterior margin of the occipita1 ring and a glabel1a, with a broadly rounded anterior, which stops well short of the anterior margin of the cranidium. However, the preservation is not adequate to war­rant formal description of the material and the erection of either a new species or a new genus.