Revision of the Trilobite Genus Calodiscus Howell, 1935 (Siberian Platform)

Trilobites of the genus Calodiscus Howell, 1935 from the Lower Cambrian of the Siberian Platform are revised. It is shown that two of the four species described from the Lower Botomian (Lower Cambrian) of the General Stratigraphic Scale of Russia, C. helena (Walcott, 1889) and C. granulosus Jegorova et Shabanov, 1972, differ significantly from typical representatives of the genus. The assignment of these species to a new genus, Paracalodiscus, in the family Weymouthiidae Kobayashi, 1943, is substantiated. The other two species (Calodiscus resimus Repina, 1972, and C. schucherti (Matthew, 1896)), although they also show some differences from the type species, are retained in Calodiscus Howell, 1935.