REMAINS OF REPTILES AND FISHES. 95 



Note. — It is on tlie palatal tooth, or plate of Ctenodus, pro- 

 bably of Ctenodus obliqims (or, perhaps, C. elegans, or it may be 

 on a minute plate of one of the larger species) that Prof. Owen 

 has founded his genus Saganodus (pi. 12). This is one of the 

 genera on which no remark was made in the " Criticism" of the 

 "Abstract ; " but a mere glance at the figure in the paper is suf- 

 ficient to satisfy us that it represents nothing else than a small 

 imperfect palatal plate of this genus. One of the authors of the 

 present communication has had in his cabinet for many years 

 numerous sections of the palatal plates of C. obliquus ; and on 

 comparing them with the figure of the "teeth and a small por- 

 tion of the jaw" of the so-called Saganodus, no diiference of the 

 slightest importance can be perceived. The six wedge-shaped 

 ridges seen in transverse section stand up from the bony net- 

 work of the plate in the form of conical tooth-like processes, all 

 inclined a little to one side, and increasing in size towards the 

 same side, and having their reticulated substance continuous with 

 that of the plate. In all these respects the resemblance to the 

 figure is so great that no one can doubt for a moment that the 

 so-called jaw and teeth of Saganodus are identical with the pa- 

 latal tooth of one of the Ctenodi. 



In the example figured by Prof. Owen, as also in many of our 

 specimens, the external enamel and the peripheral walls of con- 

 tinuous matter have been worn away. His section is evidently 

 a little diagonal, as proved by the increased depth of the plate 

 ("jawbone"). And the minute structure, as rendered in fig. 3, 

 is perfectly similar to that of many of our specimens. 



In the so-called Saganodus we see a remarkable example of 

 the danger of trusting entirely to sections of minute objects, the 

 planes of which are not understood. The oral armature of Cte- 

 nodus we have seen is composed of plates having on the surface 

 several transverse wedge-shaped ridges, which are usually denti- 

 culated or tuberculated. Had it been understood that the speci- 

 men examined was a section cutting such ridges transversely, it 

 never could have been described as a fragment of a "jaw sup- 

 porting conical teeth." 



It has been already stated that the enamel is frequently worn 



