Dr. Mantell, in his classical work, the “Fossils of the South Downs,” figured two large compressed and lanciform teeth preserved in his collection and obtained from the Chalk at Lewes, as respectively the teeth, of an unknown fish and of a species of Squalus. Similar teeth, and from the same collection, were subsequently figured and described by Prof. Louis Agassiz, who, from external characters chiefly, considered them to have belonged to a Sphyrænoid fish, and he referred them to an American species founded by Dr. Harlan upon portions of jaws with teeth in situ found in a Cretaceous deposit in the State of New Jersey, but described by him as remains of a Saurian, and to which he gave the name of Saurocephalus lanciformis. At the time when Agassiz referred these teeth to Harlan's species, and determined their ichthyic character, he had not seen the American fossils; but he states that these conclusions were subsequently confirmed by Prof. Owen's description and drawings of the microscopic structure, and of teeth of the natural size of the Saurocephalus lanciformis, Harl., in his “Odontography,” p. 130, pl. 55. But Prof. Owen's researches were made upon a genuine tooth of the American fossil sent to him by Dr. Harlan, and not upon an English specimen.