Specimen description :

Order

Phacopida

SALTER 1864

Occurrence: Lower Ordovician (Tremadoc) to Upper Devonian (Famennian).

• Cephalon: Proparian (Phacopina and Cheirurina), gonatoparian (Calymenina) or opisthoparian (Calymenina),
• Preglabellar field often very short or absent.
• 4 or fewer pairs of glabellar furrows.
• Eyes : when present, schizochroal (Phacopina) or holochroal (Cheirurina and Calymenina).
• With rostral plates (Calymenina and Cheirurina) or without (some Phacopina).
• Hypostome conterminant (all suborders) to impendent (some devonian Phacopina).
• Exosqueletton generally granulous.
• Thorax: 8 – 19 segments, sometimes distinctly furrowed.
• Axis sometimes broad (e.g., Homalonotidae).
• Pygidium : Typically micropygous (most Calymenina and Phacopina), but variable (e.g., subisopygous in Dalmanitoidea and Acastoidea).
• May be lobed or spiny (e.g., Cheirurina, some Dalmanitoidea, Acastoidea), or smooth-margined, with round or subtriangular outline (e.g., Calymenina, Phacopoidea).

Sub-order

Phacopina

STRUVE 1959

• Cephalon : Proparian sutures (sometimes fused).
• Schizochroal eyes.
• Glabella expands forwards.
• Librigena typically yoked as single piece.
• Hypostome conterminant to impendent, some with no rostral plate.
• Some with genal spines.
• Thorax: 10 to (typically) 11 segments.
• Pleurae furrowed, articulating facets distinct.
• Rounded, angular, or spinose tips.
• Pygidium : Typically smaller than cephalon (but subisopygous in Dalmanitoidea and Acastoidea).
• Smooth or spinose.

Super-family

Acastoiedea

DELO 1935

• Cephalon : Axial furrows slightly to moderately divergent.
• Anterior glabellar lobes and furrows usually not fused (although furrows may be indistinct).
• Eyes typically distant from posterior border furrows, but not strongly anterior.
• Frontal glabellar lobe auxilliary impression system triangular in outline.
• Maximum width of glabella adjacent to preglabellar furrow.
• Median region of glabella devoid of muscle scars.
• Cephalic margin "shouldered".
• Laterally convex course of genal margin topographically distinct from curvature of axial margin.
• Thorax : Pleural endings blunt, rounded or angular.
• Sometimes spinose.
• Pygidium : Micropygous to subisopygous.
• Sometimes spinose (expressed as marginal spines).
• Pygidial axis with deep, apodemal anterior ring furrows, with abrupt transition to shallow posterior ring furrows.
• Coincident decrease in angle of axial furrow convergence.

Family

Acastidae

EDGECOMBE 1993

• Cephalon : Semi-circular to rounded subtriangular.
• Cephalic border narrow in front of the glabella.
• Dorsal furrows slilghtly to moderately divergent.
• Anterior glabellar furrows (S3) simple.
• Medial furrows (S2) moderately deep.
• Deep posterior furrows (S1).
• L2 and L3 lateral glabellar lobes generally fused distally.
• Muscle scars bearing sometimes callosities (Acastinae).
• Eyes typically distant from the posterior genal furrows.
• Hypostoma
• Pygidium : micropygous to subisopygous.
• Semi-circular to rounded subtriangular.
• Short posterior spine present.

Sub-family

DELO 1935

Traditionnally included in the Dalmanitidae, Asteropyginae are now included in the Acastids. Mostly benthic trilobites.

• Cephalon : Closely similar to the Dalamanatid Dalmanitides BARRANDE 1853.
• Glabella expanding forward.
• 3 lateral glabellar furrows.
• Eyes generally large.
• Genal angles acutely pointed or bearing medium-length to very long genal spines in straight continuation of lateral margins.
• Pygidium : Rachis never reaching the posterior region of the pygidial border.
• Generally 5 pairs of lateral spines (sometimes 4 or 6).
• Unpaired posterior lappet or spine.

Genus

Psychopyge

G. & H. TERMIER 1950

Large sized Asteropyginæ, similar to Comura (comura) R. & E. RICHTER.

• Cephalon : Lack of eye ridges.
• Pygidium : Ogival.
• Axis ending with a terminal posterior piece.
• 11 to 21 rachidial segments.
• Length of the pleural ribs increasing from the 1st to the 5th.
• Interpleural furrows widening abaxialy.

Species

elegans

G. & H. TERMIER 1950

• Cephalon : Caracterized by a very long median cephalic point.
• Pygidium : Large, of ogival outline, as broad as long.
• 18 axial rings bearing a median tubercle.
• 5 pairs of lateral pygidial spines increasing in length.
• Median spine shorter than the 5th lateral pair of lateral spines.

Frontal view of the cephalon de face. Lack of subocular crest (rim?)

Anterior branch of the facial suture.

Palpebral view of the cranidium.

Side view of the specimen