Trimerocephalus

Trimerocephalus is a genus of eyeless trilobites from the order Phacopida, family Phacopidae. It lived during the final stage of the Devonian, the Famennian, and became extinct at the end of this stage, together with all other trilobites with the exception of some Proetida. It can be found in Australia, the Czech Republic, France, Germany, Iran, Kazakhstan, Morocco, Poland, the Russian Federation (Urals), Spain, and the United Kingdom (England).
Distribution.
Species belonging to the genus "Trimerocephalus" have been found in Europe, Morocco, Iran and Australia. 
Taxonomy.
"Acuticryphops" is probably ancestral to "Trimerocephalus", and mainly differs from its descendants in having an eye lobe with a small number of lenses. Crônier, 2003, erected the subgenus "Trimerocephalus (Trifoliops)" containing "T. trifolius" and "T. nigritus". In order not to be polyphyletic, "T. (Trifoliops)" would need to include at least "T. steinachensis", and preferably "T. dianopsoides" as well. These species are in the same clade as "T. mastophtalmus" however, which is the type of the genus "Trimerocephalus", which would by definition be in the nominal subgenus "Trimerocephalus (Trimerocephalus)". This in turn would prompt the erection of another subgenus with all remaining species shown in the cladogram.
Description.
"Trimerocephalus" is one of several phacopid genera that is eyeless (others being "Dianops", "Ductina", and "Trimerocephaloides"). The dorsal facial sutures are not functional, so cranidia and free cheeks (or librigenae) are not found separated. The marginal ridge bordering the cheeks is wide and convex. The part of the margin that is tucked-under (or doublure) and only visible when viewing the cephalon from the belly (or ventral side), is short and flat. The vincular furrow, a groove that fits the margin of the tailpiece or pygidium when the animal was enrolled, is wide and deep. The pygidium is about 3 times wider than long.