120 ON THE DENTAL BOXES OF CTENODTJS. 



new tooth, which I proTisionally named Petalodopsis. Through 

 the kindness of Mr. AV. Macleay, who supplied me with two 

 vomerine and two palatal teeth, I have had the opportunity of 

 examining the structure of the vomerine teeth of Ceratodws 

 under the microscope. I made a vertical section, and was pleased 

 to find that the fundamental structure was similar to that which 

 I have just described. Still there are marked points of difference, 

 for in Ceratodus the tissue is greater in quantity than the sum 

 of the diameters of the canals, and the calcigerous tubules are 

 not feathered, but they do branch as we observed the tubules in 

 the palatal and mandibular teeth of Ctenodus to do. Exter- 

 nally also the incisor teeth of Ctenodus and Ceraiodus are 

 essentially similar, both being e^'idently constructed to answer 

 the same purpose. In minutiae, however, there are differences 

 by which one could easily distinguish the one from the other. 



Judging from the anatomical, microscopical, and palseonto- 

 logical evidence before us, we can have little doubt concerning 

 the teeth I have just described. They pertain to Ctenodus, and 

 so far as we have progressed in the descriptions of the different 

 parts of Ctenodus the evidence is strengthened that Ctenodus is 

 closely allied to Ceratodus. 



Part IV. 



ON THE DETsTARY, ARTICULAR, A^'D PTERYGO- 

 PALATINE BONES OF CTENODUS. 

 By W. J. Barkas, M.E.C.S.E., L.E.C.P.L. 



\^ead before the Royal Society of Is.S.lV., 1 Novemher, 1876.] 



We have now to leave those characters of this fish that are 

 strictly dental, and enter upon the description of the different 

 parts of its osseous structure, or rather, of those parts of it that 

 are kno^T.i to us, for a portion of the endo-skeleton has yet to be 

 discovered, and necessarily many parts will not have been 

 capable of fossilization. In the previous portions of this series 

 of papers I showed that, in the external characters of the teeth of 

 Ctenodus and also in their structure, there were many points of 

 resemblance to the dental features of Ceratodus. To-night I 

 intend to speak of the dental bones, more especially, pointing 

 out their osteological characters, and incidentally I shall draw 

 attention to the dental arrangements. We viiW then see that 

 even in these points the similarity is pretty closely carried out 

 between Ctenodus and Ceratodus. 



