''Weymouthia'' is an extinct

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...

of eodiscinid agnostid

trilobite Trilobites (; meaning "three lobes") are extinct marine arthropods that form the class Trilobita. Trilobites form one of the earliest-known groups of arthropods. The first appearance of trilobites in the fossil record defines the base of the ...

s, which lived at the end of the

Lower Cambrian The Cambrian Period ( ; sometimes symbolized Ꞓ) was the first geological period of the Paleozoic Era, and of the Phanerozoic Eon. The Cambrian lasted 53.4 million years from the end of the preceding Ediacaran Period 538.8 million years ago ( ...

, in what are now the eastern United States, England, Siberia and China.

Description

Like all Agnostida, ''Weymouthia'' is diminutive and the headshield (or cephalon) and tailshield (or

pygidium The pygidium (plural pygidia) is the posterior body part or shield of crustaceans and some other arthropods, such as insects and the extinct trilobites. In groups other than insects, it contains the anus and, in females, the ovipositor. It is compo ...

) are of approximately the same size (or isopygous) and outline. Like all Weymouthiidae, ''Weymouthia'' lacks eyes and rupture lines (or sutures). The headshield (or cephalon) is approximately as long as wide, lacks facial sutures and is eyeless. The tailshield (or

) is about 1.2× as wide as long. Both are effaced except for a furrow close to their borders. The cephalic border bears lateral tubercles. The thorax consists of three segments.WHITTINGTON, H. B. ''et al''. Part O, Treatise on Invertebrate Paleontology. Revised, Volume 1 – Trilobita – Introduction, Order Agnostida, Order Redlichiida. 1997

Etymology

''Weymouthia'' is named after

Weymouth, Massachusetts ("To Work Is to Conquer") , image_map = Norfolk County Massachusetts incorporated and unincorporated areas Weymouth highlighted.svg , mapsize = 250px , map_caption = Location in Norfolk County in Massa ...

Distribution

* ''W. nobilis'' occurs in the Lower Cambrian of Massachusetts (Hoppin Slate, North Attleboro), and of the United Kingdom (Comley Quarry, Comley, 52.6° N, 2.8° W).

Remarks

Fletcher & Theokritoff (2008) designated Shaw's (1950, pl. 79, fig. 24) specimen of “ ''Weymouthia nobilis'' (Ford, 1872)” as the holotype of a new species, ''Serrodiscus weymouthioides'', and considered ''Runcinodiscus'' Rushton (in Bassett ''et al''., 1976) ?''Weymouthia nobilis'' (Ford, 1872)to be a junior synonym of ''Serrodiscus''; Rushton (1976) had previously regarded ''Weymouthia'' and ''Runcinodiscus'' as closely allied with ''Serrodiscus''. ''Weymouthia nobilis'' (Ford 1872), first described from the Taconic region of New York State, is also recorded from the ''Protolenus'' Limestone (Ac5) rotolenid-Strenuellid Zoneat Comley, Shropshire, England (Cobbold 1931),COBBOLD, E. S. 1931: Additional fossils from the cambrian rocks of Comley, Shropshire. ''Q. J. Geo/. Soc. Lond.'' 87, pp. 459 - 511 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).

References

Weymouthiidae Agnostida genera Cambrian trilobites Cambrian trilobites of Europe {{agnostida-stub Cambrian genus extinctions