Abstract

The larger cryptostome Bryozoa from the late Ordovician and early and middle Silurian strata of Anticosti Island when studied by thin section techniques consist of 9 species, 2 of which are new, Ptilodictya denticulata and Pachydictya n. sp. Seven of the species had previously been given a total of 16 names. Ptilodictya denticulata is restricted to the English lead formation upper Ordovician) and Phaenopora superba first appears in the Becscie formation (lower Silurian) and extends into the overlying Gun River formation (lower Silurian). The other cryptostome bryozoan species range from the late Ordovician into the early and middle Silurian strata except for 2 species of Stictopora which are found only in the upper Ordovician. Comparison of the bryozoan faunas and other Anticosti Island faunal elements with those in other areas from late Ordovician and early Silurian strata suggests the English Head, Vaureal, and Ellis Bay formations are equivalent in age to the Richmond group, Ohio, and it does not support the placement of these Anticosti beds into a "Gamachian series" of post-Richmond but pre-Silurian age. Based on skeletal microstructures observed in type material and additional material, the 5 species of Ptilodictya and one species of Stictoporella, S. excellens, described in this paper may be conveniently assigned to the informal taxonomic category of the escharoporid group.

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