352 Messrs. Hancock & Attliej on Reptile- and Fish-Remains 



rarely present, or are perhaps frequently buried in the matrix. 

 They are placed at some little distance from each other ; and 

 the small external teeth, like those of the upper jaw, frequently 

 exhibit considerable irregularity, though on the whole they 

 are placed apart at pretty regular intervals. The above de- 

 scription of the jaws applies to those of the usual size ; but we 

 have a mandibular bone which, if complete, would be upwards 

 of three inches long, and a maxillary or two of corresponding 

 dimensions. 



The laniary teeth are grooved at the base ; and here the 

 peripheral dentine is a little infolded or plicated ; and in fine 

 specimens the sm-face 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 

 species is worth recording. Several of our specimens were 

 found concealed within the stems of reed-like plants, which 

 bear somewhat the appearance of calamites. A single indivi- 

 dual occurred in each stem, nearly filling it. How they got 

 into this position, whether accidentally or otherwise, it is im- 

 possible to form an opinion ; but as, out of a score of indivi- 

 daals that have been fornid, four or five have been so placed, 

 it would seem that something 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 Rhizodopsis sauroides that Prof. Owen has 

 founded his Dittodas parallelus^ Ganolodus Craggesii, Chara- 

 codus confertus^ and the Batrachian genus Gastrodus. The 

 figure of Dittodus parallelus (pi. 1) seems to us to repre- 

 sent nothing more than a fragment of either a mandible or 

 maxilla of this fish, with a few pairs of the teeth in juxta- 

 position, the rest having been removed 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 den- 

 tine 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 " Siamese twins." We have now before us numerous sec- 

 tions, many of which were made several years ago, demon- 

 strating 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 



