High-resolution trilobite stratigraphy of the Lower–Middle Ordovician Öland Series of BaltoscandiaPärnaste, Helje; Bergström, Jan; Zhiyi, ZhouGeological magazine2012 / p. 1-10 : ill https://pubs.geoscienceworld.org/geolmag/article-abstract/150/3/509/299539/High-resolution-trilobite-stratigraphy-of-the

Trilobites and biofacies in the Early-Middle Ordovician of Baltica and a brief comparison with the Yangtze PlateBergström, Jan; Pärnaste, Helje; Zhiyi, ZhouEstonian journal of earth sciences2013 / p. 205-230 : ill https://artiklid.elnet.ee/record=b2651566*est