This reconstruction is based on Walcott's work using serial thin sections, announced in 1876 and summarized in Walcott (1881). This paper summarized seven years of work studying thin sections of enrolled specimens of Calymene (now Flexicalymene) senaria, Ceraurus pleurexanthemus, Isotelus gigas and Acidaspis. Some of these thin sections are reproduced in Bonino & Kier (2010).