Abstract

A new agelacrinitid edrioasteroid, Multiplexidiscus mckenziensis n. gen., n. sp. is described from the middle Silurian upper McKenzie Shale Member of the Mifflintown Formation of Pennsylvania. These edrioasteroids were attached to a large hardground clast that was reworked and flipped during a storm event. The occurrence of edrioasteroids in a near shore, perhaps in sub-normal salinity, is unusual for echinoderms. The edrioasteroids show a dispersed spatial distribution and weak thecal orientation. Multiplexidiscus differs from other agelacrinid edrioasteroids in the presence of a complex pattern of ambulacral cover plates combined with nearly straight paedomorphic ambulacra.

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