0:f THE GEKUS CTENODUS. 107 



polished ; between the ridges and the plate of attachment there 

 IS a distinct line of pale enamel surrounding the tooth ; the 

 plate of the tooth is thin ; under surface as convex as upper 

 is concave. A description of the tooth appeared in the second 

 volume of " vScientific Opinion," and an illustration was given in 

 " Coal Measure Palseontology." In my opinion this tooth more 

 closely resembles O. cristatus than C. tiiberculatus. !Fig. lY. is 

 a copy of Mr. Barkas's lithograj^h. 



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

 Measures. It was described and figured in the paper and book 

 just referred to. The tooth is 2\ inches long ; 1\ inch broad ; 

 five bold radiating ridges ; first ridge projecting forward at an 

 angle of 30 degrees, second at 45 degrees, third at 60 degrees, 

 fourth at right angles to the base, fifth inclined backwards from 

 the perpendicular 15 degrees ; ridges smooth ; tip of first ridge 

 lost ; second, third, and fourth ridges have each two highly 

 enamelled tubercles at their extremities ; fifth ridge one tubercle ; 

 the plate extends beyond the 5th ridge with an undulating 

 surface for half an inch, and is symmetrically rounded ofi" ; upon 

 the front of the tooth and opposite the groove of the fifth ridge is a 

 large mammillary tubercle or horn which distinguishes this tooth 

 from any other species. Pig. V. is a copy of the published drawing. 



The teeth I have described so far have all ridges that are more 

 or less tuberculated ; those I now intend to refer to are without 

 tubercles, and therefore more closely resemble the teeth of 

 Ceratodus. 



C. imhricatus, Atthey. Prom the Northumberland Coal Shales, 

 was described in the 3rd, and figured in the 4th volumes of the 

 Northumberland and Durham Natural History Society Transac- 

 tions, by Messrs. Hancock and Atthey. The palatal tooth is 

 depressed; very thick; slightly concave ; 2i inches long; upwards 

 of 1 inch broad ; inner margin well and regularly arched, the 

 anterior slope being much longer than the posterior : outer mar- 

 gin nearly straight and coarsely serra-ted by the ridges projecting ; 

 6 ridges, which enlarge rapidly towards the outer margin, strong, 

 smooth, somewhat distant from each other, and though mostly 

 inclined forwards, are laid over towards the posterior end, having 

 an imbricated appearance ; grooves angulated, surface minutely 

 granular, edges enamelled. Mandibular tooth very narrow and 

 fusiform ; ridges not imbricated and grooves scarcely angulated. 

 Pig. VI. is a copy of Mr. Atthey's engraving. A% my specimens 

 are in England I cannot make an original sketch. 



C. ellipticus, Atthey. From the Northumberland Coal 

 Measures, was described in Messrs. Hancock and Atthey's 

 "Notes." Palatal tooth flattened ; thin; elliptical; H inch long; 

 f of an inch broad ; inner and outer margins irregularly arched : 

 5 transverse, smooth, distant, angular ridges, increasing in size 



