Pleuroctenium


Pleuroctenium is a genus of very small agnostid trilobites whose fossils are found in Middle Cambrian-aged marine strata of Canada, Czech Republic, England and Wales, France, and Sweden. Species of Pleuroctenium can be easily distinguished from all other agnostids because the frontal lobe of the central raised area of the headshield is wider than and folds around the rear lobe.

Distribution

Like all Agnostida, Pleuroctenium is diminutive, with the headshield and tailshield of approximately the same size and outline, and only two thorax segments. The characteristic sidewise expansion of the frontal lobe of the glabella, occipital structures instead of basal lobes, and a rhachis with three pairs of side lobes and a rear lobe differentiate Condylopygidae from all other agnostids. Pleuroctenium can easily be distinguished from its sister taxon Condylopyge because the frontal glabellar lobe on both sides wraps around the rear lobe, giving it a crescent-like appearance. The frontal glabellar lobe is also generally weakly dissected lengthwise, unlike in Condylopyge. The glabella may carry spines. The pygidium may carry a pair of stout, backwardly directed spines and in some exquisitely preserved specimen, the lateral side of the pygidium and the large spines carried up to 30 minute laterally directed secundairy spines.