A Westward Extension of the Upper Ashgillian Hirnantia Fauna

The very distinctive Hirnantia fauna of uppermost Ordovician age is here recorded from Ireland, where it is found in association with the upper parts of the Chair of Kildare reef limestone. The most important hrachiopod members of the Hirnantia assemblage are Cliftoma, Cryptothyrella, Plectothyrella, Hirnantia, Eostropheodonta, and Dalmanella which are illustrated and their occurrences at other European localities indicated and discussed, particularly with respect to their differing abundances. The nature of the fauna, in conjunction with some lithological pointers, indicates a shallow water lagoonal environment of deposition. With respect to the Kildare succession, the presence of the Hirnantia fauna indicates that the upper part of the Kildare limestone at least belongs to Zone 8 of the Ashgillian; and it is believed that the North of England Keisley Limestone is also of this age, rather than of Lower or Middle Ashgillian age.