alliansidid
Alliansidid is a monotypic genus of extinct trilobites that belongs to the order Phacopida within the class Trilobita. The fossil record places its single species, Alliansidid silvestrii, in the Silurian period, approximately 430 million years ago. The genus was first described by the Italian paleontologist Luigi Maria d’Artri in 1934 based on specimens collected from the Valdai Hills of Russia. The generic name derives from the Latin "allian" meaning "joined" and the suffix "-sidid" common to trilobite nomenclature, reflecting the distinctive thoracic segments that appear fused in lateral view.
Morphologically, Alliansidid silvestrii displays a relatively small cephalon with a smooth glabella and fine spines along
Geographic distribution of Alliansidid fossils is limited to the Baltica region, with additional finds reported from