Morphometric study of the Ordovician proetid trilobite Cyamella stensioei Owens, 1978

The genus Cyamella was first described by Owens in 1978 as Cyamops, but was renamed (Owens in Owens and Hammann, 1990, p. 240) as the original genus name was preoccupied. Cyamella stensioei Owens is a small proetide trilobite from the Boda Limestone of the Siljan District in Dalarna (Sweden). The Boda Limestone (Upper Ordovician) is regarded as a carbonate mud mound showing core and flank facies (Jaanusson, 1982). Mass accumulations of trilobites within the Boda Limestone are regarded as a result of sedimentary infill and are termed pockets or cavities (Suzuki and Bergström, 1999). To our knowledge C. stensioei has not yet been described from outside these limited areas within the mounds. One rock specimen from the Boda Limestone in the quarry at Kallholn (NW part of the Siljan Ring between Orsa and Skattungsbyn) is investigated here. The aim of this study is to trace any morphometric variation of the proetid exoskeletons in one of such pockets, assuming this being a case of one particular accumulation and therefore representing variation in morphology within a species during as short a time period as possible