Weymouthia is an extinct genus of eodiscinid agnostid trilobites which lived at the end of the Lower Cambrian.

Its fossils are found in Lower Cambrian marine strata from what are now the eastern United States, England, Siberia and China.

Like all Agnostida, Weymouthia is diminutive and the headshield (or cephalon) and tailshield (or pygidium) are of approximately the same size (or isopygous) and outline.

The headshield (or cephalon) is approximately as long as wide, lacks facial sutures and is eyeless.

Weymouthia nobilis (Ford 1872), first described from the Taconic region of New York State, is also recorded from the Protolenus Limestone (Ac5) [Protolenid-Strenuellid Zone] at Comley, Shropshire, England (Cobbold 1931),>[8] but Rushton (in Bassett et al., 1976, p. 637) showed that the English specimens are specifically distinct from W. nobilis as described by Ford (1872), and thus erected his new genus and species, Runcinodiscus index Rushton (in Bassett et al. 1976, p. 636-7).