50 ^. T. Newton — Iguanodon in the Lower Chalk. 



gone no subsequent attrition. The greatest length of the portion 

 preserved is about 0-6 inch, and its width from before backwards 

 05 inch, whilst the greatest thickness, at the fractured end, is about 

 0-4 inch. The enamelled surface is somewhat pointed at the apex, 

 and has a single crest, extending from top to bottom, which divides 

 this surface into two unequal areas. The anterior and posterior 

 margins are ornamented with strong serrations, from which grooves 

 extend, almost vertically, some distance on to the enamelled surface. 

 When viewed from before, the crown is wedge-like, and the serra- 

 tions of the edge, when seen with a lens, are found not to be simple, 

 but each of them is itself denticulated, giving a mammillated 

 appeai'ance to the somewhat thickened edge. The enamel is slightly 

 roughened by small vermiform rugse. 



The close resemblance between this tooth, so far as preserved, and 

 some of those figured by Sir R. Owen ^ as Iguanodon Mantelli, woukl 

 lead to the inference that it belonged to the same species were it not 

 that one of these (figs. 15, 16) having only a single ridge on the 

 enamelled surface, has more recently been referred by Prof. Seeley * 

 and Mr. Lydekker^ to Tracliodon (Hadrosaiirus), and as our 

 specimen has only a single ridge, it would seem, at first sight, that 

 it also should be referred to Trachodon. However, Sir R, Owen's 

 figures 10 and 17 have only small secondary ridges of the enamel, 

 and these do not extend far from the base of the tooth, our specimen 

 therefore might well be a portion of such a tooth with the small 

 ridges broken away. Besides this, another tooth with only a single 

 enamel ridge, which is from the Wealden, is called Iguanodon by 

 Sir R. Owen,* and no one seems to have questioned the correctness 

 of this determination. 



Then, again, with regard to the serrations, these are coarser than 

 in the figures of Trachodon,^ and the grooves extend from them some 

 distance over the enamelled surface, a character seemingly wanting 

 in Tracliodon. The mammillations of the serrations find their 

 counterpart in both Iguanodon Mantelli and Trachodon {Hadrosaurus) 

 Fonllcei. 



The Dinosaurian remains from the Maestricht Chalk described by 

 Prof. Seeley and M. L. Dollo include certain bones which are said 

 to have affinities with Iguanodon and Hadrosaurus ; they have been 

 named Orthomerus Dolloi. It is possible that the tooth from the 

 " Totternhoe Stone " may prove to belong to the last-named genus ; 

 but as there is no evidence at present of the teeth of Orthomerus, it 

 would scarcely be wise to refer our specimen to it ; on the other hand, 

 it is quite certain, that in whatever genus this tooth may eventually 

 have to be placed, it is very closely related to Iguanodon, and with 

 this it will provisionally be included, and named specifically after 

 its donor Iguanodon Hillii. 



* Pal. Soc. Cret. Kept, suppl. ii. pi. vii. figs 10. 15, 16, 17. 



2 Q.,T.G.S. vol. XXXV. p. 591, 18?9. » Q.J.G.S. vol. xliv. p. 47, 1888. 



* Pal. Soc. Eept. Wealden, pt. ii. pi. xviii. fig. 6, 1855. 



* Leidy, Smithsonian Contributions, vol. xiv. 1865. 



