Keywords palaeoecology, Lower Carboniferous, Oichnus, Amphoracrinus INTRODUCTION Small round holes, that is, the ichnogenus Oichnus Bromley 1981, are a common phenomenon in Phanerozoic shelly substrates. These ichnofossils may be either penetrative, most commonly where the substrate is a thin shell and interpreted as predatory or parasitic in origin, or non-penetrative. The former commonly occur singly, as, with rare exceptions, it is not necessary for a predator/parasite to make more than one point of entry into its victim. Non-penetrative Oichnus may be either single or multiple. Multiple infestations in echinoderms may be particularly distinctive, being associated with growth deformities, either externally (e.g., Eckert, 1988; Eckert and Brett, 2001, pl. 9, figs. 14-17) or internally (Donovan and Jagt, 2002). Such infestations in the fossil record of echinoderms are best known from crinoids and echinoids. The paleoecology of these associations is equivocal, but sufficient information may be available to interpret the relationship of the epizoobiont (sensu Taylor and Wilson, 2002) and its echinoderm substrate (e.g., Donovan, 1991). Herein, we describe and interpret an infestation of multiple, non-penetrative Oichnus paraboloides Bromley 1981, in the Lower Carboniferous crinoid Amphoracrinus gilbertsoni (Phillips 1836), which, we consider, permits some confident Stephen K. Donovan Department of Palaeontology, Nationaal Natuurhistorisch Museum, Leiden, The Netherlands David N. Lewis Department of Palaeontology, The Natural History Museum, London, England Paul Kabrna Barnoldswick, Lancashire, England interpretations of the paleoecology of the infesting organism, although its biological affinities remain obscure. Our philosophy of ichnotaxonomy follows that of Pickerill (1994); specifically, Tremichnus Brett, 1985, is considered to be a junior synonym of Oichnus Bromley (Pickerill and Donovan, 1998). The described specimen is registered in the fossil echinoderm collections of The Natural History Museum, London, BMNH EE 8728. LOCALITY AND HORIZON BMNH EE 8728 (Fig. 1) was collected by P. K. from Salthill Quarry, Clitheroe, Lancashire [grid reference SD 7550 4265], an important locality for Lower Carboniferous echinoderms in northwestern England (Donovan et al., 2003). The crinoid theca was found in the Cover Mudstone, which occurs at the top of the lower Viséan (=upper Chadian) Salthill Cap Beds of the Bellman Limestone Member (Riley,1990). The Cover Mudstone is a distinctive, fissile mudrock yielding abundant, well-preserved crinoids. DESCRIPTION OF INFESTATION Amphoracrinus gilbertsoni (e.g.,Wright, 1954, pp. 194-197) and O. paraboloides are both well known taxa for which adequate descriptions are already available in the literature. This description will concentrate on the pattern of infestation of pits on the crinoid theca (Fig. 1) and will not reiterate the morphology of the trace and body fossils, except as it impinges on the interpretation of the paleoecology. The theca preserves the dorsal cup, fixed arms and tegmen. Oichnus paraboloides occurs on all plates of the dorsal cup (basal and radial circlets), not including the articular facet for Address correspondence to Stephen K. Donovan Department of Palaeontology, Nationaal Natuurhistorisch Museum, Postbus 9517, NL-2300 RA Leiden, The Netherlands. E-mail: Donovan@ naturalis.nnm.nl A Dense Epizoobiontic Infestation of a Lower Carboniferous Crinoid (Amphoracrinus gilbertsoni (Phillips) by Oichnus paraboloides Bromley Ichnos, 13:1 - 3, 2006 Copyright © Taylor & Francis Group, LLC ISSN: 1042-0940 print / 1563-5236 online DO1: 10.1080/10420940500511454 ICHNOLOGIC NOTE