CHELODES AND CLOSELY-RELATED POLYPLACOPHORA (MOLLUSCA) FROM THE SILURIAN OF GOTLAND, SWEDEN

Silicified assemblages of Silurian chitons (polyplacophorans) from Got land, Sweden are dominated quantitatively by a new, Wenlock species of the long-ranging genus Chelodes; C. actinis sp. nov, is described her ein. Head sclerites, previously unknown for Chelodes, are recognized f or this species, but no tail sclerites are identified. Other Gotland C helodes species, including the type species C. bergmani, are revised. Spicuchelodes pilatis, a closely related new genus and species, is als o described. Silicification took place by delayed replacement, before significant compaction. Growth patterns of sclerites in the large popu lation of C. actinis demonstrate allometry, and are used as the basis for comparison with those patterns determined from growth lines on ind ividual sclerites of C. gotlandicus and C. cf, bergmani. Variation of individual sclerites interpreted as belonging to a single animal of C. actinis is compared with that in Recent Chiton. Sculpting of the vent ral surface in thickened sclerites of these paleoloricate chitons prov ides evidence for the musculature; this is in contrast to living, neol oricate chitons which rarely show muscle attachment features but have sutural plates to provide physical articulation of sclerites.