Temporal range: Lower Cambrian
The Calodiscidae are a family of trilobites belonging to the order Agnostida that lived during the Lower Cambrian (Botomian and Toyonian). They are small or very small, and have a thorax of two or three segments. The Hebediscidae include five genera (see box).
Like all Agnostida, the Calodiscidae are diminutive and the headshield (or cephalon) and tailshield (or pygidium) are of approximately the same size (or isopygous) and outline. The central raised area of the cephalon (or glabella) has parallel sides or tapers forward, the front being rounded and expanded, and may be divided by transverse glabellar furrows. The occipital ring is defined by a complete transverse furrow and is neither not spinose nor expanded. When present, the eye lobes are short and prominent. The thorax is only known in Chelediscus (two segments) and Sinodiscus (three segments). The pygidium has a wide, tapering axis of less than six segments.
- Whittington, H. B. (1997). Volume 1 – Trilobita – Introduction, Order Agnostida, Order Redlichiida. Treatise on Invertebrate Paleontology. Part O, Revised. pp. 390–392.
- Jell, P.A. (1975). "Australian Middle Cambrian Eodiscoids with a review of the superfamily". Palaeontographica Abteilung A. 150: 1–97. cited in Whittington, H. B. (1997). Volume 1 – Trilobita – Introduction, Order Agnostida, Order Redlichiida. Treatise on Invertebrate Paleontology. Part O, Revised. pp. 348–349.
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