Revision of the genus Abrestheria (Crustacea: Conchostraca) from the Dabeigou Formation of northern Hebei, China

摘要

Re-examination of the type specimens of the conchostracan genus Abrestheria using a scanning electron microscope (SEM) has revealed details of carapace features of important taxonomic value, which have not been described hitherto. The new characteristics include: (1) small-sized reticulations on growth lines near the umbo; (2) serrated lower margins of growth lines; (3) punctae in the even lumina of reticulations; and (4) tubercles at the lower ends of the claviform radial lirae on the growth bands of the lower parts of the carapace. Consequently, the diagnosis of Abrestheria is revised, and a discussion is also made concerning relationships between Abrestheria and closely related genera, such as Eosestheriopsis, Eosestheria and Orthestheria, which have important biostratigraphic implications.