322 Messrs. Hancock & Atthey on the Generic Identity 



XXXVII. — On the Generic Identity of Climaxodus and Ja- 

 nassa, two Fossil Fishes related to the Rays. By Albany 

 Hancock, F.L.S., and Thomas Atthey. 



[Plate XII.] 



When the paper on the teeth of GUmaxodus linguceformis was 

 published*, it was not thought desirable to hazard an opinion 

 as to their arrangement, or whether they were palatal or man- 

 dibular, or whether or not they belonged to both the upper 

 and lower jaws. Since then we have obtained information 

 that throws much light on the subject of these curious dental 

 organs. 



Mr. Howse having called our attention to some well-pre- 

 served specimens of the teeth of Janassa hituminosa of Mun- 

 sterf, from the Marl-slate, it was at once obvious, as pointed 

 out by that gentleman, that they were closely related to those 

 of Climaxodus — so closely, indeed, that they seem to be generi- 

 cally the same. The differences are only those of proportion, 

 there being not a single character of importance to distinguish 

 one from the other. 



The teeth in both forms are depressed and elongated in the 

 antero-posterior direction, and taper a little backwards ; in 

 front there is a wide concave margin, which, standing up like 

 a scoop or dredging-bucket, is the cutting-edge ; behind this 

 the surface is covered with transverse imbricated ridges, form- 

 ing the grinding or crushing portion ; and fui-ther down, on a 

 lower plane, the broad depressed root projects backwards and 

 downwards for a considerable distance. In profile they pre- 

 sent a sigmoid curve, the frontal scoop-like portion standing 

 up in the direction of the oral cavity, the posterior or root 

 extremity being turned downwards in the opposite direction. 



The above description will do equally well for either Cli- 

 maxodus or Janassa. Our Coal-measure species, however, G. 

 linguoiformis^ Atthey, is considerably wider in proportion to 

 its length, and the transverse imbricated ridges are stronger 

 and much less numerous than they are in Janassa hituminosa. 

 But G. imbricaf us, M^Coy, from the Mountain Limestone, seems 

 somewhat intermediate between the two ; it is proportionally 

 narrower, and the ridges are much finer than in G. linguce- 

 formis. 



From these teeth alone the generic identity of all the three 

 might be safely predicated ; but there is further evidence in 

 proof of the fact. Climaxodus and Janassa are both provided 

 with two kinds of teeth. Those already indicated may be 



* Annals of Nat. Hist. ser. 4. vol. ii. p. 821. 



t Beitrage ziir Petrefactenkundr, Heft 2. p. 38, tab. 15. f. 10-14. 



