Ristnacrinus and the earliest myelodactylid from the Ashgillian Boda Limestone of Sweden

Stem ossicles with synarthrial articulations (fulcral ridges) are limited to relatively few pelmatozoan groups. Columnals of Ristnacrinus sp. and Musicrinus bodae gen. et sp. nov. are of this type and have been recognized in the Boda Limestone. Ristnacrinus seems to have been widespread in Europe during the late Ordovician, although its known distribution is limited by the scarcity of crinoid columnal workers. M. bodae is the only myelodactylid inadunate crinoid known from the Ordovician. It differs from other members of this family in having a holomeric column but apparently lacking cirri. The crown and method of attachment are unknown.