OK THE GENUS CTENODUS. 105 



O. tulerculatus from the cabinet of Mr. T. P. Barkas. Alter 

 the convexity to a concavity and shorten the external ridge to a 

 uniformity with the others, and we would have an almost perfect 

 figure of G. cristatus. 



C. ohliqims, Atthey. From the jSTorthumberland Coal Measures, 

 is a comparatively common species. It has been described and 

 figured by Messrs. Hancock and Atthey in the third and fourth 

 volumes of the "Transactions " I have already alluded to, and by 

 Mr. Barkas in " Coal Measure Palaeontology." Externally the 

 tooth is plate-like ; depressed ; lanceolate ; 1^ inch long ; f inch 

 broad ; inner margin regularly and much arched ; outer border 

 slightly curved ; six or seven strong, compressed, sharp-edged, 

 transverse ridges, radiating somewhat towards the external margin, 

 where being enlarged they curve downwards and are denticulated ; 

 anterior ridge very oblique, being much inclined forwards ; 

 tubercles much compressed laterally, lancet-formed with sharp 

 points, coated with brilliant enamel ; mandibular tooth narrower 

 than palatal, is broadest in front, tapering pretty regularly pos- 

 teriorly, anterior ridges very wide and much produced beyond 

 the others, all the ridges are curved downwards, and vary from 

 f of an inch to 1^ inch in length. In figure II. I have 

 pourtrayed this tooth. 



C. elegans, Atthey, is the commonest species found in the 

 Northumberland carboniferous shales, and it is also the smallest 

 variety. It was described in the " Notes " of Messrs. Hancock 

 and Atthey, but was not figured. Mr. Barkas illustrates it in his 

 work, and I herewith give a drawing of a very large specimen, 

 Pig. III. The tooth is plate-like, depressed, triangular, averag- 

 ing f of an inch in length and -re of an inch in breadth; 

 inner margin produced and angulated in centre, from whence it 

 slopes anteriorly and posteriorly towards the outer margin, which 

 is slightly arched ; seven to eight strongly denticulated ridges 

 which radiate from the angle, at which point they are very 

 minute; anterior ridge a little produced; six or seven denticles 

 on each ridge, which are much compressed laterally, sharp- 

 pointed and lancet-like, with inner limb a little shouldered, 

 where there is occasionally a minute toothlet ; ridges and 

 denticles brilliantly enamelled. Professor Owen, in his 

 booklet on the " Dental Characters of Carboniferous Fishes and 

 Batrachians," founds a new genus, Sagenoclus, upon some sections 

 he had sent to him, but he never saw the original teeth ; the 

 structure exhibited by the microscope of these sections presented 

 features quite new to him, and he accordingly designated the tooth 

 Sagenodus ineqicalis.. In this work he gave excellent illustrations 

 of the structure, and it is similar in every detail to the micro- 

 scopical appearance of G. elegans, which had been described fully 

 long previously. 



