108 03f THE GEXTJS CTEJfODTJS. 



externally; grooves wide and round, anterior and posterior margins 

 extended a little beyond the ridges, surface minutely punctated ; 

 mandibular tooth narrow and inner border gibbous, otherwise is 

 the same as the palatal. No drawing has been published, and I 

 cannot illustrate the tooth, for the reason given above.* 



G. ohtusus, T. P. Barkas. From the Northumberland Coal 

 Measures. The palatal tooth was described by Mr. Barkas in the 

 4th volume of the " English Mechanic." The tooth is strong ; flat ;' 

 approximately ovate ; 1^ inch long ; 1 inch broad ; inner margin 

 regularly arched; outer margin has a wave-like serration arising 

 from the roundness of the extremities of the projecting ridges ; 

 the four posterior ridges and their accompanying furrows have an 

 undulating appearance, the grooves and ridges being equal in 

 width ; the anterior ridge is broad, flattened, and slightly concave ; 

 upper surface boldly punctated and ridged, the edges of which 

 have a tendency to inosculate ; much of the surface has, therefore, 

 a reticulated appearance. Mr. Barkas adds — " That the only tooth 

 with which it is likely to be confounded is O. ellipticus, but a very 

 slight examination will show the contrast that exists between 

 them." 



C. quadratus, T. P. Barkas. From the Northumberland Coal 

 Measures, was described in the 18th volume of the " English 

 Mechanic," but it has not been illustrated. The teeth of this 

 species vary slightly in size, but the tooth I figure in Fig. YII 

 is about the average ; the inner margin is bent almost at right 

 angles, a little external to its centre ; the outer margin is also bent 

 about the same place, but not so abruptly, possessing more of a 

 curve ; this peculiarity of the margins gives the tooth a quadrate 

 form ; the outer margin is irregularly waved from the ridges pro- 

 jecting beyound it ; the ridges, six or seven in number, radiate 

 from the inner angle ; they are not tuberculated, being smooth 

 and angular ; upper surface finely pitted and showing a tendency 

 to reticulation. 



C. ovahts, T. P. Barkas. From the Carboniferous Limestone of 

 Derbyshire. Only one tooth has been discovered; it was describedin 

 the 2nd volume of " Scientific Opinion," and was figured in " Coal 

 Measure Palaeontology." I have not the founder's description at 

 hand, but I herewith give a copy of his lithograph. Fig. VIII. 



C. interruptus, T. P. Barkas, was founded on a tooth in the 

 York Museum, and w^as described in the same paper as C. ovatus. 

 I cannot describe this species, for I have never seen it, nor has it 

 been figured, and as I have said, I have not at present access to 

 the 2nd volume of "Scientific Opinion." 



* This tooth has the gi*eatest resemblance to a tooth of Ceratodm ; the 

 latter tooth has six ridges instead of five, the plate does not extend beyond 

 the anterior and posterior margins, nor is it so large. 



