MANDIBULAR AND PALATAL TEETH OF CTENODTJS. 115 



It only remains for me to notice C. elegans. On account of the 

 extreme thinness of the plate of the tooth of this fish, it is impos- 

 sible to cut vertical sections similar to those we have employed in 

 observing the structure of the teeth of the other species of 

 Ctenodus. Even in taking transverse sections, it matters not how 

 carefully one may attempt to make them, it is also impossible to 

 cut below all the tubercles, which are large compared to the size 

 of the tooth ; we have, therefore, an appearance presented to us 

 of bulbous ridges ; in Fig. XII, however, the first ridge has been 

 taken pretty fairly, the bulbous aspect only appearing near its 

 apex. In a section like this we still find the two varieties of 

 structure that we noticed in C. tuberculatus ; Fig. XII, however, 

 does not exhibit the network character of the medullary canals 

 in the base of the plate of the tooth ; but I have observed that 

 feature in other specimens that have been more fortunately 

 ground ; it does illustrate, though, the vertical tendency of the 

 course of the canals in the upper part of the plate and in the 

 ridges and tubercles, for both Figs. XII and XIII show them cut 

 transversely across as they were proceeding towards the upper 

 surface. From these ^canals dentinal tubules are given off which 

 ramify in the clear osseous tissue that is observable in the centre 

 of each tubercle. The peculiar radiate form of the bone substance 

 in the centre of the tubercles is due to the medullary canals 

 grooving the mass on their course upwards, leaving processes of 

 clear transparent bone between them. External to the medullary 

 formation we have the layer of dense tissue, and covering that, in 

 unworn specimens, there is a coat of enamel. 



Part III. 



ON THE VOMERINE TEETH OF CTENODUS, 

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



\_Read before the Royal Society of N.S.W., 1 November, 1876.] 



In the spring of 1874 I discovered two teeth in the shale of the 

 Low Main Coal Seam in the Carboniferous formations of North- 

 umberland, that were quite new to me and to all Coal Measure 

 palaeontologists to whom I submitted them, and in none of the 

 numerous works to which I then had access were there any 



