''Circulocrania'' is an extinct

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...

trilobite Trilobites (; meaning "three lobes") are extinct marine arthropods that form the class Trilobita. Trilobites form one of the earliest-known groups of arthropods. The first appearance of trilobites in the fossil record defines the base of the ...

s in the family

Cyclopygidae Cyclopygidae is a family of asaphid trilobites from the Ordovician. Cyclopygids had aextratropical distribution, and there is evidence that they lived in darker parts of the water column (around 175m deep). Cyclopygids are characterized by en ...

. The genus lived during the later part of the Arenig stage of the

Ordovician Period The Ordovician ( ) is a geologic period and system, the second of six periods of the Paleozoic Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period million years ago (Mya) to the start of the Silurian Period Mya. Th ...

, approximately 478 to 471 million years ago.

References

Cyclopygidae Asaphida genera Early Ordovician trilobites of Europe Fossils of Great Britain {{Asaphida-stub