A HISTORY OF ESSEX extinct marine lizards known as Mosasauria are occasionally met with, some of these belonging to Liodon anceps, while others indicate a species more nearly allied to, if not identical with, the typical genus Mosasaurus, whose remains are so abundant in the Upper Cretaceous formation of Belgium. Very few species of fishes appear to have been hitherto recorded from the Chalk of Essex. These include Ptychodus polygyrus^ a common species of a well known Cretaceous genus of pavement-toothed rays, teeth of which have been found both at Grays and Purfleet. Three species of sharks are known, all from Grays, namely Scapanorhynchus subulatus, Corax falcatus and Oxyrbina mantelli, the latter being repre- sented in the British Museum collection by an associated series of fifty- seven teeth and some vertebra from Grays. All are common Cretaceous forms. The same locality has also yielded teeth of Enchodus leivesiensis, an extinct barracuda-like fish with large teeth, originally named on the evidence of remains from the Sussex Chalk.
