Eodiscidae


Eodiscidae is a family of agnostid trilobites that lived during the final Lower Cambrian and the Middle Cambrian. They are small or very small, and have a thorax of two or three segments. Eodiscidae includes nine genera.

Taxonomy

The Eodiscids probably descended from the agnostids of family Yukoniidae.

Description

Like other agnostids, the body of eodiscids is diminutive, the headshield and tailshield are of approximately same size, with 2 or 3 thoracic segments in-between, each consisting of a horizontal inner portion that abruptly passes into an inclined outer portion. The central raised area of the cephalon is narrow, usually with parallel sides and rounded front. The furrow between the occipital ring and the more frontal parts of the glabella are a pair of pits low on its sides beneath a large median spine extending from the glabella backwards. The distance between the glabella and the border is usually long. This border has dozens of small furrows radiating inward, but this defining feature may be absent in effaced species or destroyed by poor preservation. The axis of the pygidium has four to ten rings.