A WENLOCKIAN (SILURIAN) GASTROPOD SHELL AND OPERCULUM FROM SIBERIA

In a large collection of Wenlockian gastropods from north Siberia, a s ingle small specimen shows the operculum in situ just within the apert ure. In other morphologic features, particularly the presence of numer ous spiral lirae on the shell, this species is similar to Silurian gas tropods traditionally assigned to Oriostoma. Preservation of the operc ulum is far from perfect, but almost certainly it has paucispiral grow th, rather than concentric or multispiral construction. This new speci es (Australonema varvarae n. sp.) is assigned to Australonema, previou sly known only from the Lower Devonian of Australia, primarily because of the form of the operculum. The material was obtained from just bel ow a biostromal unit in a bed interpreted as an interreef lagoon in an area of locally relatively quiet water.