LOWER DEVONIAN CALMONIID TRILOBITES FROM THE ARGENTINE PRECORDILLERA - NEW TAXA OF THE BOULEIA GROUP, AND REMARKS ON THE TEMPO OF CALMONIIDRADIATION

New calmoniids from the Lower Devonian Talacasto Formation in the Prec ordillera of San Juan, Argentina, extend the stratigraphic and geograp hic ranges of a clade including Bouleia Kozlowski, 1923 and Paraboulei a Eldredge, 1972. The new genus Talacastops accommodates the Lochkovia n T. zarelae sp.nov. from the Talacasto Formation and a closely relate d species from western Bolivia (Talacastops sp.nov. A). The diagnosis of Parabouleia is broadened to include P. eldredgei sp.nov., from Loch kovian strata in the lower part of the Talacasto Formation. Calmoniids from below the Scaphiocoelia Assemblage Zone display morphological di sparity that rivals later occurrences, and do not conform to a model o f gradual transformation of an acastomorph ancestor. Stratigraphic ran ge extensions based on correction for ghost lineages imply a high dive rsity within Calmoniidae very early in the Devonian.