Fig. 22. Oral area of the hemicosmitoid Thomacystis tuberculata Paul, 1969, Late Ordovician, Wales, UK. Ambulacra are interpreted as B, C, D, and E and neither ambulacrum A nor plate O3, the oral associated with ambulacrum A, is developed. Facets (F) are shared by ambulacral plates the homologies of which are uncertain, and lateral plates (L1–L9). Primary ambulacral plates (O1, O2, O4, O5). Plate L4 of hemicosmitids is missing in Thomacystis and caryocrinitids (Paul 1984: 144, fig. 87). An, anus; G, gonopore; M, mouth; N, pore for presumed nerves. Redrawn and relabelled from Paul 1969: 193, fig. 2.