Fig. 13. Thecal plates of the Silurian blastozoan Lysocystites sculptus Miller, 1889, Indiana, USA, showing homologies with blastoids, coronates, and glyptocystitoids. A–E, Carpenter's (1884, 1891) ambulacra. Unknown erect ambulacra arose from facets (F) on ambulacral plates (RR), homologues of blastoid lancet plates and the radial plates of Rhombifera Barrande, 1867 (Fig. 19A3). The mouth frame is composed of five deltoids (LL, homologues of the lateral plates of Rhombifera). The periproct (P) lies in the CD interambulacrum above additional deltoid plates (white) and shares the gonopore (G). The main body of the cup is formed of five infralateral plates (ILL, homologues of blastoid radials) and three basal plates (BB). Compare with the oral view, Fig. 20B. For plate homologies see Table 2. Redrawn from Sprinkle 1973:140, fig. 34.