In 1866 Salter established this species on the basis of two somewhat distorted pygidia, but the head-shield and thorax have remained undescribed and apparently unknown. The discovery therefore by Mr. V. M. Turnbull of some complete though somewhat imperfectly preserved individuals in the Arenig Beds near Haverfordwest is of not a little interest; and with the aid of several detached head-shields, in addition to those belonging to individuals with typical pygidia, we are able to give a fairly complete description of the species, which, owing to its relations to other genera, is particularly worthy of note.