The earliest encrinurid trilobites from the East Baltic and their taxonomic interest

The earliest known representative of the subfamily Encrinurinae, Encrinuroides regularis sp. nov., is described from the glauconitic sandstone of the Ma¨eku¨la Member, Billingen Stage (Arenig), from localities in the Baltic-Ladoga Clint area. Cybele (subfamily Cybelinae) has its earliest appearance at about the same level, but at different localities, probably indicating their facies dependence. The predominant developing area of the pygidial axis and the general array of spines on the exoskeleton serve to distinguish the Encrinurinae and Cybelinae, but resolve the Staurocephalidae and Dindymeninae within the Encrinuridae. A reassessment of Encrinuroides and the genera recently excluded from it (Frencrinuroides, Physemataspis and Walencrinuroides) sustains the utility of an Encrinuroides sensu lato grouping and endorses Strusz’s evolutionary lineages. Encrinuroides uncatus Evitt and Tripp, E. neuter Evitt and Tripp and probably Encrinuroides lapworthi Tripp belong in Erratencrinurus Krueger.