36 



PROCEEDINGS OF THE 



Upjier Devonian genus Acmoniodus *, two of them, of very 

 different shape and size, are seen enihedded in a bilaterally- 

 symmetrical pentagonal plate of the soft dentine already mentioned. 

 The discovery of skeletons of the Copodontidae will prove of great 

 interest. 



In tlie Carboniferous Cochliodontidae the grinding or crushing 

 teeth have the same structure as those of the other Brady odonts, 

 but they are arranged on the rami of the jaws as in the existing 

 Cestracion. As first pointed out by Owen t, most of the antero- 



Fig. 4. 



Diagrammatio oral view of iinsymmetrical paired series of teetb oi Psammodus 

 rugosus, from the Lower Carboniferous of Armagh, Ireland, about one- 

 half nat. size. 



posterior series of the teeth differ from those of Cestracion in 

 being fused into continuous plates, each curving into a little 

 scroll at the aiuerior or outer border. The components of these 

 plates, however, have now bwn seen in many specimens which 

 are marked by partially oblireratetl sutures, and it is clear that 

 they were never more than 6 or 7 in number — thus very 

 diffei-ent from the long and rapid succession of teeth in the 

 Cestracionti(la\ The CocbliodontidiB Mere indeed Bradyodonts. 

 Nearly all the genera are known only by teeth, but the generalised 

 Helodus is represented in the AVanl Collection in the British 

 Museum by several portions of skeletons. In these fossils there is 

 no trace of the vertebi'al axis, which must have been Jiolochordal. 



* Acmoniodus clarhei, Hussakof & Bryant, Bull. Buffalo Soc. Nat. Sci. 

 vol. xii. (1'J18), p. 151. pi. 55, fig. 3. 

 t Odontography (184t»), p. ()2, 



