Ptychagnostus atavus

Order Agnostida / Suborder Agnostina / Superfamily Agnostoidea / Family Ptychagnostidae

ptych-, Greek, fold; Agnostus, a trilobite genus name.

atav-, Latin, ancestor; the author at the time considered this species the oldest agnostid of Skåne, Sweden.

Agnostus atavus; Ptychagnostus (Acidusus) acidusus; Ptychagnostus (A.) navus; Ptychagnostus acidusus; Acidusus atavus; A. acidusus

Cephalon convex, subovate; glabella conical, frontal segment subtriangular, anterior end subacutely rounded; posterior segment most convex, median node slightly behind the middle of the posterior segment; basal lobe large, distinct distinctly divided into two lobes; preglabellar median furrow present; cheek with furrow ornament, border narrow. Pygidial axis convex, divided into three rings; second ring broad medially with raised axial node; posterior axial ring long slightly longer than the sum of the anterior two rings, tapering smoothly backward; a shallow median furrow behind the pygidial axis; pleural region smooth; border broad, without marginal spines.

Typical body length about 0.2-1.2 cm, the GSSP index fossil of the Cambrian Series 3, Stage 6, i.e. the Miaolingian Drumian Stage.