WELL-PRESERVED TREMADOCIAN PRIMITIVE RADIOLARIA FROM THE WIND- FALL FORMATION OF THE ANTELOPE RANGE, EUREKA COUNTY, NEVADA, U.S.A.

Abstract

With 1 figure and 7 plates Abstract: Primitive radiolarians have been found in the upper part of the Windfall Formation (Antelope Range, Nevada), and are dated by conodonts as Cordylodus angulatus Zone (early Ibexian in North American usage = early Tremadocian in North Atlantic terms). They are the first radiolarians known from the Tremadocian. Two new families, Echidninidae n. fam. and Protoentacti- niidae n. fam. (superfam. Protoentactiniacea n. superfam.), three new genera, Noblella n. gen., Parechidnina n. gen. and Proto- entactinia n. gen. and 6 new species, Echidnina bengtsoni n. sp., Parechidnina nevadensis n. sp., Protoentactinia gracilispino- sa n. sp., P. latospinosa n. sp., P. minuta n. sp. and Noblella tremadociensis n. sp. are described. In the Echidninidae, the central space inside the loose spongy shell or protoshell is hollow. In the most primitive form, Echidnina, isolated spicules are inter- locked to form a subglobular, hollow protoshell. In Parechidnina the spicules are fused to a loose lattice. The Echidninidae are probably CoUodaria and may be the direct forerunner of the Spumellaria through forms similar to Parechidnina. The sub- globular to globular, loose spongy test of the Protoentactiniidae is formed by repeated branching of a spicule and partial fusion of the terminal branches. The basic spicule consists of a median bar and 3 or 4 terminal rays on both sides of the median bar, as is characteristic for bar-centred Entactinaria. The Protoentactiniidae are apparently the most primitive Entactinaria, but still sim- ilar to CoUodaria. Echidninidae and Protoentactiniidae are near the common root of skeleton-bearing Radiolaria.