Achritarchs of the North-west of the Russian Platform. Rozanov, A. Yu.; Missarzhevsky, V. V.Tommotian stage and the Cambrian Lower boundary problem., [Eds] Tommotian stage and the Cambrian Lower boundary problem. Trudy geol. Inst. Leningr. 206, 1969: 224-236. Chapter pagination: 224-236. 234 [Zoological Record Volume 106]