Late Ordovician rostroconchs (Mollusca) from fluvial erratics in northwestern Europe

This paper describes 3 species of ribeirioid and 2 species of conocardiid rostroconchs from fluvially transported erratics in the Dutch-German border area. The material probably stems from Ordovician deposits of the North Estonian Confacies Belt. The ribeirioid specimens from the Haljala group of erratics (Sandbian 2) are represented by Tolmachovia sublirata sp. nov., Beukeria plicata gen. nov. sp. nov. and Ischyrinia viator sp. nov. The single specimen of Tolmachovia is hitherto the youngest occurrence of this genus and the first in Baltica. The presence of subordinate radial ornamentation is added to the emended diagnosis of the genus. The new genus Beukeria is an ischyriniid rostroconch with an elongated conch, two thick pegmas and a plicate shell posterior to vertical axis. Ischyrinia viator is similar to the coeval I. norvegica Soot-Ryen, 1960 but this has a ventrolateral sinus that is subparallel to the dorsal axis. Conocardiid specimens from the Pirgu Öjlemyr chert (Katian 4) are represented by Bitrigonocardia lindstroemi (Isberg) and Pojetaconcha costulata sp. nov. The identification of Bitrigonocardia lindstroemi is circumstantial as the type specimens are missing, but as understood here new details of morphology and ornamentation are given. Pojetaconcha is for the first time recognized outside Laurentia and Australia. Pojetaconcha costulata sp. nov. is distinguished by 14 or 15 broad and flat-topped radial ribs on the body and snout and compares closely with the Chazyan P. alabamensis (Pojeta & Runnegar, 1976), USA. Ischyriniids occur mainly in Baltica with Ischyrinia migrating into Laurentia. A general exchange of Bitrigonocardia and Pojetaconcha is seen between Laurentia and Baltica.