104 ox THE GENTS CTE^'ODUS. 



of the tee til of different species of Gtenodus has ever seen them ; 

 and, as I have said, neither descriptions nor figures are extant for 

 comparison. 



C. tuherculatus was discovered by ]Mr. T. Atthej, in the 

 shale of the Low Main coal seam in jS'orthumberlaud, and was so 

 named by him. The discoverer, in conjunction with the late Mr. 

 Albany Hancock, F.L.S., describe its teeth fully in the " Notes " 

 that I have already referred to. The folloAving is a brief epitome 

 of the external characters of the tooth ; plate-like ; thick ; irregu- 

 larly ovate ; 2| inches long ; 1\ inch broad, but they vary a 

 little in size, the specimen I figure is 2^ inches long and If 

 broad ; narrow posteriorly ; inner margin gibbous or angulated 

 in the centre ; outer margin a little convex ; upper surface slightly 

 convex, with from twelve to eighteen ridges traversing it, deep, 

 sharp, parallel and approximate, strongly tuberculated towards 

 the outer margin ; grooves narrow, deep, and angular ; ridges 

 arched posteriorly and enlarged towards the external border, but 

 they are not radiate ; anterior ridge widest, and is reflected and 

 prolonged somewhat beyond outer margin ; tubercles conical with 

 obtuse points, those near the outer border are coated with 

 brilliant enamel and are well-produced; mandibular tooth narrower 

 than palatal and very convex. Erom this description it will be 

 seen that this tooth differs from C. cristatus in being convex, and 

 in having sharp and deep ridges, and by the form of the tubercles. 

 Messrs. Hancock and Atthey gave an illustration of this tooth 

 in the fourth volume of the " Transactions of the Northumberland 

 and Durham Natural History Society," but Mr. Barkas figured 

 it previously in the sixth volume of the " Greological Magazine," 

 and at the same time a drawing was given of a tooth in the 

 British Museum, with a few remarks by the editor. Mr. Barkas 

 also gives excellent lithographs in the "Atlas" to his "Coal 

 Measure Palaeontology." Mr. Miall of Leeds gave it as his 

 opinion, in the Annals of Natural History, fourth series, volume 

 15, that there is not any difference between the teeth of C. 

 iuberculatus and C. cristatus. I cannot help thinking that that 

 gentleman has never seen a true tooth of the former fish or he 

 would never have uttered this opinion, for they undoubtedly 

 differ very much, but it is possible that they might belong to the 

 one species, the one tooth being mandibular and the other 

 palatal, but this is not probable, as C. tuherculatus is compara- 

 tively common while C. cristatus is very rare ; nor have they ever 

 been found on the same slab of shale ; groups of the teeth of C. 

 iuberculatus have been discovered which tend to show that the 

 mandibular and palatal teeth are similar, the latter differing 

 from the former in being narrower only ; we must, therefore, for 

 the present at least, consider these two varieties of teeth as 

 belonging to different species. Fig. I. is a specimen of a tooth of 



