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FOSSIL REPTILIA OF THE 



serrations would appear. In some upper molars of Iguanodon the margino-serrate 

 character is continued in a minute form nearer to the base of the posterior margin. I 

 have figured a left upper molar of this variety in figs. 2, 3, 4, of PI. I, and also 

 to show the further variety of three secondary ridges on the hind facet of the crown. 



But the upper molars in the subject of fig. 9 show, as in the enlarged view (fig. 10),. 

 a continuation of the relieved or raised lateral borders across the base of the crown, in a 

 curved course, convex toward the fang. This basal ridge does not project beyond the 

 origin of the primary ridge, but falls into that origin. 



I have not observed this character, at least so definitely marked, in any upper tooth 

 of Iguanodon Mantelli, and I regard it as indicative of a specific distinction of the 

 smaller Iguanodon now under review, believing myself entitled to conclude as to it& 

 generic relationship from the characters of the dentition of the upper jaw above defined 

 and illustrated. 



It is true that one, at least, of the premaxillary teeth is canine-like with a crown 

 " lanceolate and acuminate." But no portion of the skull of Iguanodon Mantelli has yet 

 been discovered which would supply the means of testing its resemblance to or difference 

 from the smaller species, in regard to this dental character. Consequently, prior to 

 our knowledge of the skull and dentition of the smaller species, the discovery of a tooth 

 answering in size to the ordinary upper molars of Iguanodon Mantelli, but with a 

 " lanceolate and acuminate crown," would naturally suggest its reference to some other 

 Dinosaurian genus of the Wealden, of the bulk of the Iguanodon. In giving a descrip- 

 tion of this tooth in the ' Supplement on Wealden Reptilia,' in the Palseontographical 

 volume for 1857, issued in 1859 (p. 42), I therefore suggested that it might belong either 

 to Cetiosaurus or Pelorosaurus. I now, however, from its resemblance to the entire 

 premaxillary tooth in the small Iguanodon — as close as is the resemblance in the 

 maxillary teeth — deem it more probably to belong to the larger species and to be a 

 premaxillary tooth of Iguanodon Mantelli. As such, two views of this tooth of half the 

 natural size are given in PI. II, figs. 19 and 20, for comparison with the magnified view 

 of the laniary of the smaller species (fig. 18). The surface of the crown (fig. 20) which 

 answers to the outer one in fig. 18, and in i, fig. 9, PI. I, is convex both lengthwise and 

 transversely, and most so in the latter direction along the middle part ; the main or mid- 

 ridge of the maxillary Iguanodontal teeth being thus represented. On the opposite (inner) 

 side of the crown (fig. 19, PI. II) the surface is concave across the two thirds next the 

 apex. One margin, the anterior according to the analogy of the small Iguanodon, is 

 convex, the hinder margin along its terminal half is slightly concave. The crown 

 expands antero-posteriorly above the root to nearly midway to the apex, towards which 

 the borders then converge to a point with the different contours above noted. Both 

 borders are trenchant, not serrate. 



Now that we know that a laniariform, or ' lanceolate and acuminate,' premaxillary tooth 

 was associated with molars of the Iguanodontal type, in a small exemplar of the genus, 



