Revision of the type species of Acrotreta and related Lingulate brachiopods

The poorly known type species of Acrotreta, A. subconica Kutorga, 1848 [=Spondylotreta faceta Gorjansky, 1969], is redescribed and a neotype selected from the lower Arenig (Billingen Stage, Oeland Series) Päite beds in the environs of St. Petersburg (Tosna river), Russia. Acrotreta is also the type of the lingulate brachiopod family Acrotretidae Schuchert, 1893, and order Acrotretida Kuhn, 1949. Four new species are described: A. korynevskii from the upper Tremadoc–lower Arenig, South Ural Mountains; A. tallinnensis from the upper Arenig (Volkhov Stage), Tallinn, northern Estonia; A. nobilis from the Llanvirn (Kunda Stage), Siljan district, Sweden; A. cooperi from the Llandeilo, Alabama, USA. Acrotreta has many features in common with Spondylotreta Cooper, 1956. The type species of the latter, S. concentrica Cooper, 1956, from the Llandeilo Pratt Ferry beds at Pratt Ferry, Alabama, is refigured.