Trilobites of the Lower Ordovician (Ibexian) Fort Cassin Formation, Champlain Valley region, New York State and Vermont

Abstract

The Lower Ordovician (Ibexian) Fort Cassin Formation of New York State and Vermont consists mainly of carbonates that were deposited in a subtidal storm-influenced setting. The low diversity trilobite fauna is dominated overwhelmingly by the isoteline, Isoteloides. Eleven species representing at least nine genera are described; Acidiphorus whittingtoni is new. The bathyurine genus Goniotelina Whittington and Ross is regarded as paraphyletic and is synonymized with Acidiphorus Raymond. The presence of Isoteloides canalis (Whitfield; = I. latimarginatus Fortey), I. peri Fortey and Bathyurellus platypus Fortey indicates a correlation of the Fort Cassin with the Strigigenalis caudata Zone of the Catoche Formation of western Newfoundland.