Mathesius liaoningensis, a new genus and species of Cleroidea, probably relative of clerid or thaneroclerid branches of the superfamily, is described from the Lower Cretaceous; it belongs among the oldest and the best preserved cleroid fossils that have been known so far. The unique specimen was found in Yixian Formation (ca. 125 Ma) near Huangbanjigou Village, Beipiao City, Liaoning Province, NE China and belongs to the famous Chinese Jehol Biota. A classification of Mathesius liaoningensis gen. et sp. nov. within Cleroidea is based on cucujiform aedeagus with distinct medial apodeme (strut) and probably paired struts of the phallobase, pentamerous mesoand metatarsi, narrowly separated proand mesocoxae, metacoxae extending laterally to meet elytra. A possible relationship with the clerid or thaneroclerid branches is based on predacious mandibles, absence of large spines in tibiae, lobes at least in mesoand metatarsomeres 2–3 (probably 1–4), probably six visible abdominal ventrites, and shape of body. With the exception of the aforementioned features, the well-preserved fossil shows interesting morphological characters which are figured in detail and discussed in the context of morphology of some recent cucujiform families.
New adherent foraminiferans from the Lower Cretaceous (Aptian) of south-central England