316 T. P. Barkas — On Ctenodus from the Coal-shale. 



portion to the size of the fish that the opercular plate of G. cristatus 

 does to the fish to which it belonged, it must have been, according 

 to the estimation of competent paleeontologists, little short of ten 

 feet in length. I have not yet discovered any palate teeth of a size 

 proportioned to opercular plates so large as that just described ; the 

 largest tooth I have obtained, and, I have reason to believe, the 

 largest that has been obtained anywhere, is a palatal tooth, which, 

 provisionally, I ascribe to Ctenodus tuberculatus, although it in some 

 respects differs materially from the description of that species given 

 in the '' Annals of Natural History." 



In order to afford an opportunity of estimating the appearance 

 and size of teeth of this species, figures are annexed (see Plate IX.) 

 of a palatal (Fig. 2) and mandibular tooth (Fig 1). 



Fig. 2 represents a palatal tooth, and Fig. 1 a mandibu^lar tooth 

 (both of the natural size) with the mandible attached and in situ. 

 The figures represent teeth belonging to the same species, and al- 

 though they were not obtained on the same day, it is not improbable 

 that both belonged to the same fish — their sizes, state of preser- 

 vation and general appearance so closely resemble each other. Of 

 the teeth of C. tuberculatus I have but three specimens, those figured 

 and a fragment of a mandibular tooth which has eight perfect ridges, 

 one of which I have removed for the purpose of making a section 

 for microscopic examination. The bony texture of the tooth is ex- 

 ceedingly hard, the base being very open and cellular ; but the 

 exterior grinding portion being dense, thick and hard, it must 

 have offered a formidable surface for crushing food during the 

 lifetime of the fish. This excessive hardness of the outer enamel 

 will account for the fact that the greater proportion of the palatal and 

 mandibular teeth that have been found are as perfect, sharp, and well- 

 defined as though they had never been used. The cellular portions 

 of the teeth and plates of attachment of the Ctenodi bear consider- 

 able resemblance to the Pleurodi and Poecilodi in their microscopic 

 structure. 



Of Ctenodus corrugatus I have not found a single specimen ; the 

 only remains of that species with which I am acquainted being a 

 palatal tooth, which is preserved in the Museum of the Natural 

 History Society of Newcastle-on-Tyne. The tooth is crossed by nine 

 irregular, corrugated ridges, and is remarkably unlike the teeth of 

 any other known species of Ctenodi. I have obtained about two 

 hundred specimens of C. elegans, C. obliquus, C. imbricatus, and G. 

 ellipticus, several of which have been presented to museums and 

 private palaeontologists. In my collection there are also three 

 specimens with four ridges, probably new to science, and many 

 specimens respecting which I have not yet obtained any satisfactory 

 information. 



EXPLANATION OF PLATE IX.— Figs. 1 and 2. 



Fig. 1. — Mandibular tooth of Ctenodm tuberculatus. 

 „ 2. — Palatal tooth of same, 



both from the Coal-shale of Newsham Colliery. 



