Mallagnostus Howell, 1935, HOWELL, B. F. 1935. Cambrian and Ordovician trilobites from Herault, southern France. Journal of Paleontology 9 (3): 222-238 is a trilobite genus belonging to the family Weymouthiidae Kobayashi T. (1943), KOBAYASHI, 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. Order Agnostida Salter (1864) 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. according to Whittington et al. 1997. WHITTINGTON, H. B. et al. Part O, Treatise on Invertebrate Paleontology. Revised, Volume 1 – Trilobita – Introduction, Order Agnostida, Order Redlichiida. 1997. It lived during the late Lower Cambrian, with remains found in USA (New York), Canada (Newfoundland), Spain, England, Russia (Tuva, Gorno-Altayskaya), Mongolia, and the early Middle Cambrian as reported from China (Tian Shan) and Russia (Yakutia).
Taxonomy Mallagnostus was originally described as belonging to the Agnostina, but it is more appropriately placed in the Eodiscina. Within the Weymouthiidae, Mallagnostus belongs to a clade that further includes Tannudiscus, Jinghediscus and the Agnostina.
Distribution M. desideratus Walcott, 1890, WALCOTT 1890. Descriptive notes of new genera and species from the Lower Cambrian or Olenellus zone of North America. Proceedings of the United States National Museum, 12: 33 - 46. is from the Lower Cambrian Olenellus Zone of North America. M. limbatus Pokrovskaya, 1959, POKROVSKAYA N. V., 1959. The trilobite fauna and stratigraphy of the Cambrian deposits of Tuva. Akademiy Nauk, SSSR, Trudy, Geologisicheskogo, Instituta, Number 27, pp. 1-199, pls. 1-11. [In Russian]. has been collected from the upper Lower Cambrian of New York, WHITTINGTON, H. B. et al. Part O, Treatise on Invertebrate Paleontology. Revised, Volume 1 – Trilobita – Introduction, Order Agnostida, Order Redlichiida. 1997 and the Toyonian of the Russian Federation (Obruchev stage, Shivelig Formation, Shivelig-Khem River, Tuva, Altay-Sayan, Siberia, 51.4° N, 94.2° E) cited in M. llarenai Richter and Richter, 1941, RICHTER, R., & RICHTER, E., 1941. Die Fauna des Unter-Kambriums von Cala in Andalusien. Abhandlungen der senckenbergischen naturforschenden Gesellschaft, 455: 90 pp., 83 figs., 4 pls., Frankfurt. is found in the late Lower Cambrian of Spain (serratus Band, Herrerias-Mergel Formation, Cala).
Ecology Mallagnostus limbatus occurs with Tannudiscus tannuolaicus, Menneraspis striata, Beldirella pulchra and Cheiruroides maslovi.
Description Mallagnostus is isopygous and, like all Weymouthiidae, lacks eyes and facial sutures. The cephalon is semi-elliptical with unfurrowed glabella (in one species there are lateral indentations). The glabella does not quite reach the broad border furrow. The occipital ring (L0) is short (sag.), ill-defined, and does not carry a spine. Anterior border of cephalon is long, only gently convex, and becomes shallower further from the axis. The border furrow runs into the margin just in front of the genal angle. Thorax of three segments, as in all other Weymouthiidae where the thorax is known. The pygidial axis is conical with at least eight rings, and does not extend to the posterior border furrow. Pleural fields smooth.
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