Silicified trilobites of the genus Sphaerocoryphe from the Middle Ordovician of Virginia

Abstract

Two similar species of Sphaerocoryphe, Sphaerocoryphe gemina sp.nov. and Sphaerocoryphe longispina sp.nov., from the Edinburg Formation (Blackriveran) of northwest Virginia are described. The most conspicuous differences lie in the pygidia. The protaspis closely resembles that of Ceraurinella; transitory pygidia are allocated to degrees one to eight, and the first appearance of the great spines provides a useful marker. Two ontogenetic series can be recognized, culminating in the two adult morphologies, and ruling out the possibility of a single dimorphic species. There are two profixigenal spines in meraspid cranidia up to 2.5 mm in sagittal length, one pair in larger cranidia of both species. The smallest hypostome possesses two lateral spines, later reduced to one. Hemisphaerocoryphe Reed is considered a junior subjective synonym of Sphaerocoryphe Angelin. The 29 named species are compared.