CRETACEOUS FORMATIONS. 57 



the teeth of the Crocodile, direct evidence to that effect had not been obtained at the 

 time of the publication of my ' Report on British Fossil Reptiles ;' and it has been 

 objected that the mode of fixation of the teeth of the Polyptychodon might have 

 been the same as in the Mosasaurus, and that those teeth might belong to a second 

 extinct genus of gigantic Sea-lizards. The specimen, however, which is represented 

 of the natural size in T. X, fig. 3, inclines the balance in favour of the Crocodilian 

 affinities of the Polyptychodon, by proving that its teeth were implanted in distinct 

 sockets, and not anchylosed to the summits of processes of the jaw, as in Mosasaurus 

 and Leiodon. In the figure cited, taken from an unique specimen of part of the lower 

 jaw of the Polyptychodon interruptus discovered in the lower chalk-deposits of Kent, and 

 now in the collection of Mrs. Smith, of Tonbridge Wells, the letter b shows the 

 smooth cement-covered cylindrical base, and c the enamelled conical crown ; s is an 

 adjoining vacant alveolus, from which a tooth similar to that in place has slipped out, 

 like the teeth from the Lewes Chalk-marl. The crown of the tooth in place is rather 

 longer in proportion than in most of the detached teeth from Lewes ; and it may, 

 therefore, indicate a certain inequality in the length of the crowns of the teeth in the 

 same jaw, as in the Crocodiles, and it may have answered to the tooth which is some- 

 times called, on account of its greater length, the " canine tooth" in the Crocodile. The 

 socket anterior to the one with the completed tooth contains the germ of a young 

 tooth, e, and shows that the teeth succeeded each other from the same sockets as in 

 the modern Crocodiles. 



The crown of a much larger tooth of the Polyp lychodon interruptus, which is figured 

 in Tab. IX, figs. 16 and 17, was found near Valmer, during the cutting of the Lewes 

 railway, and. is now in the museum of Henry Catt, Esq., F.G.S., of Brighton. It 

 shows well that alternate and interrupted character of the longitudinal ridges of the 

 enamelled surface which distinguishes the present species, but the ridges have been 

 more worn down, especially towards the apex, in Mr. Catt's specimen, than in the one 

 originally figured in my ' Odontography.'* The body of the crown consists of a hard 

 compact dentine, partly resolved in the specimen by incipient decomposition into 

 superimposed hollow cones, like the similarly-sized tooth of the Polyptychodon continuus 

 from Mr. Bensted's Green-sand " Iguanodon" quarry at Maidstone. f The cylindrical 

 case of the tooth is excavated by a wide conical pulp-cavity with an obtuse summit, 

 into which a small central process projects from the base of the crown (fig. 17). The 

 enamel is very thin at the base of the crown. 



Figure 8 in Tab. XI, is the crown and part of the base of a still larger tooth of 

 apparently the same species of Polyptychodon obtained by Mr. Catt in October 1850, from 

 the grand and picturesque chalk-pit, or rather chalk-cliff, at Houghton, near Arundel. 



* Odontography, pi. lxxii, figs. 4, 4', 



f lb. fig. 3, and 'Report on British Fossil Reptiles,' p. 156. 



