Paralejurus dormitzeri

 

Specimen description

  • Complete, prone, specimen.
  • On matrix.
  • Lenses very distinct.
  • Strong contrast between trilobite and matrix.
  • Total length : 80 mm.
  • Devonian
  • Morocco.
  • NB : Both cephalon and pygidium present terrace lines perfectly ditinct.
Lateral view.
Dorsal view

 

Diagnose :

 

Order

Corynexochida

 KOBAYASHI 1935 Occurrence: Lower Cambrian – Middle Devonian
  • 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

 JAANUSSON 1959

Occurence du Cambrien supérieur jusqu'au Dévonien.

  • Céphalon : Typically effaced.
  • Doublure broad.
  • Opisthoparian facial sutures.
  • Sutures distinctly divergent anteriorly.
  • Glabella expands forwards.
  • Lateral furrows often faint or absent.
  • 4 pairs of glabellar furrows, commonly faint or absent.
  • Extra-axial cephalic muscle impression (lunette) present.
  • Eyes frequently on the posterior part of the genae, close to the axial furrows.
  • Frequent terrace lines, particularly on 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 for the late species of Panderia.
  • Frequent fainting of the trilobitation.
  • Thorax : 8-10 segments.
  • Pygidium : Isopygous or subisopygous.
  • Rounded posteriorly.
  • Usually with short axis.

Superfamily

 Illænoidea HAWLE & CORDA (1847)  
Family Styginidæ (=Scutelluidæ) VODGES (1890)

Earlier forms :

  • Cephalon : Glabella narrowest just in front of occipital ring, expanding forward.
  • Glabelle devoid of glabellar furrows or of muscular impressions.
  • Pygidium : Stout.
  • Rachis narrow.
  • Doublure narrow.

Later forms:

  • Cephalon : Frontal lobe strongly expanding .
  • Hypostoma shield shaped with subtriangular body.
  • Posterior lobe of the hypostoma well developped with very marked maculæ.
  • Pygidium : At least as wide as long.
  • Axis short, usually with trilobitation.
  • Doublure broad.
Genus Paralejurus HAWLE & CORDA (1847)

Exoskeleton vaulted.

  • Cephalon : Strongly vaulted.
  • Broad glabella, anteriorly expanding.
  • absent or faint dorsal furrows.
  • Small acicular librigenæ.
  • Occipital furrow and ring very broad (tr.)
  • Rostral plate large, very convex.
  • Thorax : Axis much broader than pleuræ.
  • Pygidium : Bell-shaped and almost smooth.
  • Rachis mostly indistinct,without trilobitation.
  • Ribs broad, flat, only separated by thin intercostal furrows.
  • Doublure moderately broad.
  • Shell thick
Species dormitzeri ?
  • Pygidium : parabolic.
  • Large (sag.).
  • Very convex.
  • 7 pairs of convex ribs.

 

Complementary pictures :

 

Rarely seen on Paralejurus dormitzeri : the tiny lenses are all perfectly seen.
Frontal view : vaulted cephalon, terrace lines.

 

Complementary specimen :

 

 

Specimen description

  • Complete specimen.
  • on matrix, but partly free.
  • Ocular lenses not seen.
  • Cuticular terraces perfectly seen, notably on the cephlaic and pygidial doublures (concentric).
  • Length : 75 mm.
  • Devonian
  • Morocco
  • NB : Trilobite in "U posture", considered to be a resting posture.
Lateral view.
Dorsal view.

 

Ventral view of the cephalon : concentric terrace lines on the doublure.
Ventral view of the pygidium : idem.

 

Dorsal view of the pygidium : ribs and thin intercostal furrows.

 

Precisions and remarks :

 

1) This trilobite in particular, amongst moroccan trilobite, is very frequently faked.Fakes and real specimens are generally easy to distinguisj, but one has to keep humble :) REMEMBER that a specimen sold for a ridiculous price is higly doubtfull. The specimens described here should not been paid less than 60 dollars, neither more than 120, btw ;)

2) Here are 2 obvious examples of these (partial) fakes/assemblages that are frequently found on Ebay or in exhibits ... (BTW, it is sad that such dealers are still admitted in even once a fakery has been proven).

 

 

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