Stigmadiscus Explained

Stigmadiscus Rasetti, 1966,^[1] is a genus of Lower Cambrian Eodiscinid trilobite belonging to the family Weymouthiidae Kobayashi (1943) ^[2] Order Agnostida (Salter 1864) ^[3] It lived during the Botomian stage, = late Lower Cambrian Stage 4 (upper of two stages subdividing the un-named Series 2); the upper Botomian Stage boundary corresponds to base of both the Middle Cambrian Wuliuan stage and Miaolingian Series.

Stigmadiscus resembles Acidiscus in having a relatively short glabella, distinct S1 and S2 lateral furrows, and a slender occipital spine. In fact, according to Cotton & Fortey (2005, fig. 3) ^[4] consensus is that Stigmadiscus and Bolboparia Rasetti, 1966, are sister taxa of Acidiscus.

Notes and References

1. RASETTI, F. (1966). "New Lower Cambrian trilobite faunule from the Taconic sequence of New York". Smithsonian Miscellaneous Collections. 148 (9): 1–52.
2. KOBAYASHI T. 1943. Brief notes on the Eodiscids 1, their classification with a description of a new species and a new variety, Proceedings of the Imperial Academy, Tokyo, Volume 19, pp. 37-42.
3. SALTER, J. W. 1864: On some new fossils from the Lingula - flags of Wales. Quarterly Journal of the Geological Society of London, 20, 233 – 241.
4. COTTON, T. J. and FORTEY, R. A. (2005). "5. Comparative morphology and relationships of the Agnostida". In Koenemann, S.; Jenner, R. (eds.). Crustacean Issues 16, Crustacea and Arthropod Relationships. Boca Raton: CRC Press.