REMAINS OF EEPTILES AND FISHES. 89 



the surface of the crown exhibits a thin film of enamel. Traces 

 of enamel, too, are occasionally found on the small teeth ; but 

 they are most frequently without it, probably in consequence of 

 erosion. 



One curious fact in connexion with the occurrence of this spe- 

 cies is worth recording. Several of our specimens were found 

 concealed within the stems of reed-like plants, which have some- 

 what the appearance of Calamites. A single individual occurred 

 in each stem, nearly filling it. How they got into this position, 

 whether accidentally or otherwise, it is impossible to form an 

 opinion ; but as out of a score of individuals that have been 

 found four or five have been so placed, it would seem that some- 

 thing more than mere chance has had to do with it. 



Note. — It is apparently on fragments of the jaw bones and on 

 the teeth of Piliizodoijsis sauroides that Prof. Owen has founded 

 his Dittodus paraUehis, Ganolodus Craggesii, Characodus confer- 

 tus, and the Batrachian genus Gastrodus. The figure of Ditto- 

 dus 2)(irallelus (pi. 1) seems to us to represent nothing more than 

 a fragment of either a mandible or maxilla of this fish, with a 

 few pa,irs of the teeth in juxtaposition, the rest having been re- 

 moved either before deposition or in making the section. 



When two teeth grow up close together, as we have seen is 

 not unfrequently the case in this species, the peripheral dentine 

 of the two is often united at the base, and then we have a "twin 

 tooth" in all respects similar to those figured of this so-called 

 Dittodus, and just as well entitled to be compared to the " Sia- 

 mese twins." We have now before us numerous sections, many 

 of which were made several years ago, demonstrating this fact ; 

 and in one or two instances there are even three or four teeth 

 so united. 



That which is denominated " osteo-dentine," in the apical 

 part of the pulp cavity, is, we apprehend, a mere film of the 

 inner layer of dentine. A similar substance occurs in many of 

 our sections, exhibiting the general appearance and dotted struc- 

 ture given to it in Prof. Owen's figure ; and this is undoubtedly 



