122 ox THE DENTAL EONES OF CTENODrS. 



Opinion" or tlie " English Mechanic," I am not now sure to which 

 nor have I access to them to find out, but in that letter he 

 remarks that he has evidence to show that in one case at least 

 the mandible and maxiUary bones had each two teeth ; however 

 this may be, it is the general, if not universal rule, that each of 

 these bones carry only one tooth. Putting aside the exceptional 

 example mentioned by Mr. T. P. Barkas, no marked difference 

 can be observed between this mandible and the mandible or 

 dentary bone of Ceratodus ; the similarity is carried further, in 

 that both these genera have the lower jaw composed of two 

 osseous portions, an inner or dentary bone and an outer or 

 articular bone, which in the modern fish are held together by an 

 intervening mass of cartilage and were presumably so united in 

 the palaeozoic fish. It was only recently that the articular 

 bone was discovered, or rather, the bone had been found 

 some time by Mr. Atthey, but he did not recognize it until 

 he had had the opportunity of examining the articular bone 

 of Ceratodus. In 1874 he verified his belief, for he dis- 

 covered two specimens of the mandibular arrangement of C. 

 ohliqims, in which the dentary and articular bones were in their 

 natural positions. These articular bones I have observed in the 

 cabinet of Mr. T. P. Barkas, and I have one in my possession. 

 It is this specimen that I pourtray in Fig. XXII. - In describing 

 this bone, Mr. Atthey states that it varies much in length — as 

 much as from f of an inch to finches; he then proceeds : — 

 " The articular bone of Otenodus is of about the same length as 

 the inner plate or ramus which bears the teeth, slightly convex 

 on the outer surface, and marked by five or six apertures for 

 vessels ; it is pointed upwards in front like the prow of a boat. 

 Its posterior border presents two scallops, the upper being some- 

 what larger than the lower, which extends to the posteriorly 

 projecting point of the lower border, which is convex ; the 

 upper scallop ends at a rounded projection, which separates it 

 from the upper border. Tliis border presents two shallow con- 

 cavities, the anterior occupying the greater part of the border ; 

 the posterior has a projection on its inner side, somewhat in the 

 form of a bracket, for the support of the teeth of the inner 

 plate or ramus." In the bone that I figure there are some 

 slight points of difference from the above description, the 

 inferior margin is not so ciuwed anteriorly ; the upper concavity 

 on the posterior border is not so large as the lower one, nor 

 does the superior margin present two conca^-ities. "With these 

 minor exceptions, however, my specimen agrees with his account. 



The pterygo-palatine bone (Pig. XXIII.) is a flat bone, situated 

 along the front and sides of the roof of the mouth, having its 

 antero-posterior diameter much greater than its lateral diameter ; 

 its posterior extremity is much more expanded than its anterior. 



