Plesiosaur skulls: Elasmosaurus, Plesiosaurus, and Trinacromerum, all from side, Samuel Wendell Williston, 1925

Illustration of plesiosaur skulls (elasmosaurus, plesiosaurus, and trinacromerum) from the osteology of the reptiles (1925). Date: 1925. The Osteology of the Reptiles p58