MORROWAN LITHISTID DEOSPONGES AND HEXACTINELLIDS FROM THE OZARK MOUNTAINS OF NORTHWESTERN ARKANSAS

Silicified and well-preserved specimens of the new orchocladine anthas pidellid genus and species, Virgaspongia ichnata, the rhizomorine hapl istiid, Haplistion sphaericum Finks, 1960, and various root tufts, and the new hexactinellid species Steioderma hadra are reported from the Brentwood Member of the Morrowan Bloyd Formation from the Sulphur City quadrangle, in the Ozark Mountains of northwestern Arkansas. Virgaspo ngia is a subcylindrical branched or unbranched sponge that lacks a sp ongocoel and has a dendroclone-based skeleton in which trabs diverge u pward and outward from an axial region. It is abundant here but is one of only a few anthaspidellid genera known from the Pennsylvanian. Thi s is the first record of Haplistion from Pennsylvanian rocks of Arkans as, although the genus is widespread in upper Paleozoic rocks. The new hexactinellid species, Stioderma hadra, also documents the first occu rrence of that genus from Arkansas and in Morrowan rocks. Only fragmen ts were recovered but the swollen grotesque spicules, of several sizes , that make the fused dermal layer and outer sponge wall are distincti ve, particularly where combined with an inner layer(?) or root tuft of monaxons of various sizes. Two different root tufts and one demospong e wall fragment(?) also occur in the collection.