378 CRETACEOUS REPTILES. 
Description of the Fossil Reptiles of the Chalk Formation. 
By Proressor Owen, F.R.S. 
Class REPTILIA. 
Order CROCODILIA. 
Genus PotyprycHopon. 
Species. Polyptychodon interruptus (Tab. XXXVII. figs. 16 & 17, and 
Tab. XXXVIII. fig. 3). 
It appears from the evidence of detached teeth that a Saurian reptile as large 
as, if not identical with, the one whose massive remains were discovered by 
Mr. Mackeson in the greensand near Hythe, and to which I have given the 
generic name Polyptychodon*, existed during the period of the deposition of 
the chalk. 
The fine crown of one of these teeth, which was found near Valmer in cutting 
the Lewes railway, and is now in the museum of Henry Catt, Esq., of Brighton, 
is represented of the natural size in Tab. XXXVII. figs. 16 &17. It shows that 
alternate and interrupted character of the longitudinal ridges of the enameled 
surface which distinguishes the species called Polyptychodon interruptus + ; 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 greensand 
‘Teuanodon’ quarry at Maidstone}. The cylindrical base 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. 
The affinities of the remarkable Saurian genus Polyptychodon, on which the 
* Report on British Fossil Reptiles, p. 157. + Odontography, pl. 72. figs. 4, 4’. 
{ Jb. fig. 3, and ‘Report on British Fossil Reptiles,’ p. 156. 
