Aulacopleura

Aulacopleura is a genus of proetid trilobite that lived from the Middle Ordovician to the Middle Devonian. Some authors may classify this group as subgenus "Otarion (Aulacopleura)".
The cephalon is semicircular or semielliptical, with border and preglabellar field. The glabella is short, with or without defined eye ridges connecting it with eyes of variable size. Spines at the rear outer corners of the cephalon (or genal spines) are present, typically reaching back to the 2nd to 4th thorax segment. The 'palate' (or hypostome) is not connected to the dorsal shield of the cephalon (or natant). The cephalon is pitted, or has small tubercles. The thorax has up to 22 segments. The pleural ends are usually rounded. The pygidium is small (micropygous), with an even margin. "A. koninckii" had a modern type of compound eye.
Taxonomy.
Barrande described "Arethusa koninckii" in 1846. However, "Arethusa" was occupied since it was used by De Montfort in 1808 for a foram protist. Barrande tried to correct this by proposing "Arethusina" as a replacement, but by that time that Hawle and Corda had already suggested "Aulacopleura" in 1847, which is thus the senior available name.