Page:VCH Surrey 1.djvu/68

 A HISTORY OF SURREY its many-ridged teeth being uniformly conical instead of more or less distinctly trihedral. The second reptile is a huge marine turtle allied to the existing leathery turtle (Dermatocbelys) ; it was named by the present writer 1 Protostega anglica on the evidence of two imperfect specimens of the upper arm-bone (humerus) in the British Museum, one of which was obtained from the chalk of Lewes and the other from that of Dorking. In several geological works it is stated that remains of another reptile, Mosasaurus graci/ts, have been met with in the chalk of the county. These, however, are now known to belong to fishes of the genus Pacbyrhizodus, whose teeth are of unusual size and strength. Some of the most common fish-remains that occur in the Surrey chalk are the well-known crushing palatal teeth of rays of the genus Ptychodus, of which several species are represented in the county. Of Ptychodus mammillaris the British Museum possesses twenty associated teeth in a block of chalk from Guildford, and likewise an associated set of twenty-three teeth obtained from the same locality in 1851 ; in addition to these there are also teeth from the chalk of Dorking. In the same collection there are likewise teeth of Pt. rugosus from Guildford, of Pt. decurrens from Dorking, as well as of Pt. polygyrus from a chalk-pit on St. Catherine's Hill near Guildford, while, there is a single large tooth of Pt. latissimus from Croydon and a smaller one referable to the same species from Guildford. A Cretaceous ray belonging to the genus Squatina is represented in the national collection by several vertebra? from the chalk of Dorking. Among sharks, a tooth from the chalk of Guildford in the British Museum is referable to Notidanus microdon, one of the comb-toothed representatives of the group. In the same collection are an associated set of eleven vertebrae and a fin-spine from Guildford, as well as a tooth from Warlingham near Croydon, referable to Cestracion rugosus, a com- paratively rare species of pavement-toothed shark, nearly related to the living Australian representative of the genus. Another type of pavement-toothed shark is represented by Synecbodus illingivortbi (formerly known as Acrodus] of which the British Museum possesses teeth from the chalk of Guildford and Dorking. Among other sharks Scapanorhynchus rhaphiodon is represented in the national collection by teeth from the upper chalk of Shalford near Guildford, and Purley near Croydon, as well as by others from the lower chalk of Guildford. Scapanorhynchus was long regarded as an extinct type, but it appears closely allied to, if not identical with, a living Japanese form described as Mitsikurina. Of porbeagle sharks (Lamna) the British Museum con- tains teeth from Surrey belonging to two species, L. sulcata and L. appendi- culata, the latter being frequently referred to as Otodus appendiculatus. Two teeth from the lower chalk of Guildford in the same collection are assigned to the nearly related Oxyrbina angustidens, while the remains of 1 Catalo&te Fossil Reptilia British Museum, pt. iii. p. 229 (1889). 30