Specimen description

Order

Corynexochida

• Cephalon: Opisthoparian sutures.
• Glabella elongate, sides often concave (pestle-shaped).
• Furrows (when not effaced) typically with splayed arrangement, the hind pair pointing sharply backwards. Anterior pairs tending more and more forward directed. Sometimes furrows pit-like.
• Cranidial borders often ledgelike.
• Hypostome conterminant or (in derived forms) impendent.
• Eyes typically large, in some gently arcuate
• Thorax: typically with 7-8 segments (but range for order is 2-12, rarely more).
• Pleural tips often spinose.
• Pygidium : typically large (isopygous or subisopygous).
• Variable form.
• Some spinose.

Suborder

Illænina

Occurence : Upper Cambrian Devonian.

• Cephalon : Typically effaced.
• Doublure broad.
• Opisthoparian facial sutures.
• Sutures distinctly diverging anteriorly.
• Glabella expanding forwards.
• Lateral furrows often faint or absent.
• 4 pairs of glabellar furrows, commonly faint or absent.
• Extra-axial cephalic muscle impressions (lunette) present.
• Eyes frequently on the posterior part of the genæ, close to the axial furrows.
• Terrace lines frequent, particularly at the distal ends of the thoracic exoskeleton and the ventral doublure.
• Hypostome impendent (conterminant, but hypostome no longer matching anterior glabellar border)
• Rostral plate limited by sutures, fused in the late species of Panderia.
• Trilobitation frequently fainting .
• Thorax : 8-10 segments.
• Pygidium : Isopygous or subisopygous.
• Rounded posteriorly.
• Usually with short axis.

Superfamily

• Cephalon : Axial region of cephalon smooth, merging forward into frontal area without boundary.
• 4 pairs of muscle scars can be observed instead of glabellar and occipital furrows.
• Glabella strongly convex.
• Opisthoparian facial sutures.
• Rostral shield broad (tr.).
• Hypostoma oval, with elongated body (sag.)
• Anterior wings of hypostoma broad, quadrangular.
• Pygidium : Axis and pleural field smooth or with very faint traces of unfurrowed ribs.
• Surface ornemented with terrace lines or small pits, or both.
• No tuberculate or granulose ornementation.

• Cephalon : Significantly larger than the pygidium and has a length two thirds the width.
• Most prominently convex at the center.
• Eyes set well back and far apart.
• Free cheeks with a prominent blunt angle.
• Thorax :8 thoracic segments
• Aaxial lobe about one third the width of the whole trilobite.
• Pygidium : Relatively small, having a length two thirds that of the cephalon and a width twice that of the length.
• Strong axial furrows that are well defined over half the length of the pygidium which continue through the thorax and end on the cephalon as sigmoid curves (curving in then out).
• Surface is covered with short squamose (“resembling a scale”) wrinkles.