EARLY SILURIAN RADIOLARIA FROM NORTHERN NEVADA, USA

Radiolarians recovered from three sites in the early Llandoverian Cher ry Spring chert, north-central Nevada, provide the first Early Siluria n radiolarian data from the conterminous United States. Two assemblage s were recovered that contain abundant pylomate sphaerellarians, rotas phaerids, inaniguttids, and possible palaeoactinosphaerids. The pyloma te taxa have an intermediate spine morphology with Cessipylorum and Ac iferopylorum, bringing into question the present criteria for distingu ishing these two genera. Rotasphaerids include both species of Rotasph aera and Secuicollacta, that have five primary rods per spine unit, si milar to those present in Ordovician assemblages (Caradocian-Ashgillia n) reported from Nevada and Australia. Oriundogutta is another common component shared between the Cherry Spring and Caradocian-Ashgillian a ge faunas. To a lesser extent. the Cherry Spring fauna resembles late Early-Late Silurian (Wenlockian-Ludlovian) assemblages that contain ab undant inaniguttids and rotasphaerids. None of the younger species of inaniguttids have been recognized, however, and younger species of rot asphaerids differ in that they have six primary rods per spine unit an d a more diverse spine morphology. These preliminary data indicate a s tronger similarity between Late Ordovician and early Llandoverian asse mblages than between early Llandoverian and Wenlockian-Ludlovian assem blages. The Cherry Spring chert faunas contain several distinct forms, such as Cessipylorum(?) sp. A and B, that may prove useful for biostr atigraphic correlation.