Fig. 4.

Fossil specimens. (A) Scleral plate belonging to Ctenacanthussp. CMNH 5956. Dotted line indicates the boundary of the scleral plate. (B) Partial scleral ring of Cladoselachesp. CMNH 8324 composed of many small rectangular plates (single plate indicated by arrowhead). (C) Gymnotrachleus hydei scleral plate, CMNH 8053, crescent-shaped with tapered ends. (D) Four Titanichthyssp. sclerotic plates arranged into a sclerotic ring. (E,F) Heintzichthys gouldiisclerotic ring CMNH 5291. All scale bars are 10 mm.