Conulariid microfossils from the Silurian Lower Visby Beds of Gotland, Sweden

A conulariid fauna from the Lower Visby Beds (uppermost Llandovery-lowermost Wenlock) is described, based on microscopic exoskeletal parts found in limestones and marls prepared using standard laboratory techniques for phosphatic fossils. Although not a single complete conulariid specimen has ever been found in the unit, conulariids were evidently abundant during the deposition of the Lower Visby Beds, as inferred from the microscopic fragments. So far, five species have been identified: Conularia sarae sp. nov., C. wimani sp. nov., C. sp. a, Metaconularia aspersa, and Pseudoconularia aff. scalaris. The microscopic fragments exhibit considerable external morphological variation. They can be sorted into four discernible morphological groups, and their position in the exoskeleton can be identified. Thus, more or less complete reconstructions of the exoskeletons have been made on species unknown prior to this investigation. Characters used in species descriptions based on intact specimens are summarized and compared with characters used for microscopic fragments. The conclusion is that the general ornamentation of the exoskeleton is the most useful character in species descriptions. Moreover, microscopic fragments are not only as easily identifiable as intact specimens, but due to the fact that a larger quantity of material is obtainable, the study of microscopic fragments also gives a far better picture of the individual variation, ontogenetic development, geographical range and the stratigraphical range of conulariid species. Finally, some existing morphological terminology is modified and some new terms are introduced.