Description du spécimen

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 : Dorsal furrows almost rectilinear.
• Eyes very small or absent.
• Post-ocular branches of the facial sutures curved at their posterior end.
• Subtriangular hypostoma.
• Anterior border of the hypostoma almost transverse or slightly bent forward in its central part.
• Anterior wings broad and short.
• Thorax : 10 segments.
• Axis well defined.
• Pygidium : About half of the cephalon's length (sag.)
• Doublure as long as 30 to 50 % of the pygidium total length (sag.)

Large sized isopygous form (up to 30 cm).

• Cephalon : parabolic.
• Almost smooth.
• 5 faint pairs of muscle scars (see below)
• Dorsal furrows faint, completely fainting exsagittally at the anterior half.
• Very small eyes, located at the posterior part of the cranidium.
• Librigenæ narrow and subtriangular.
• No genal spines.
• Cephalic doublure broad with concentric terrace lines.
• Rostral plate of large size, semilunar, with transverse sutures.
• Hypostoma quadratic with subtriangular body, sharp and covered with terrace lines.
• Anterior wings broad (tr.), quadrangular.
• Cephalic angle : 80 to 85°.
• Thorax : 10 segments
• Quadratic rings, as wide as the third of the total width.
• Smooth pleuræ, bearing a geniculation at mid-length.
• Pygidium : slightly ogival, almost circular.
• Axis hardly distinct.
• Pygidial angle : 110 to 120°