Subrder HALYSITINA Upper-Ordovician - upper Silurian. Corallites are enclosed into ranks, which are meandering or form polygonal lacunae. Corallites are separated in ranks by coenenchymal tubuli (Halysites, Fig. 4A) or by dissepiments (Cystihalysites, Fig. 4B). Commonly corallites have a common wall in ranks without coenenchymal tissue (Catenipora, Fig. 4C). They are abundant in the Ordovician and Silurian outcrops of West-Estonia (Catenipora tractabilis, Catenipora quadrata and Halysites junior).