ON CLIMAXODUS AND JANASSA. 331 



or dredging-bucket, is tlie cutting edge ; behind tbis the surface 

 is covered with transverse imbricated ridges, forming the grind- 

 ing or crushing portion ; and further down, on a lower plane, 

 the broad depressed root projects backwards and downwards 

 for a considerable distance. In profile they present 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 Cliviaxo- 

 clus or Janassa. Our Coal-Measure species, however, C. lingiue- 

 formis, 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 bituminosa. But C. imhri- 

 caius, M'Coy, from the Mountain-Limestone, seems somewhat 

 intermediate between the two : it is proportionally narrower, 

 and the ridges are much finer than in C. linguaformis. 



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 looked 

 upon as the principal or primary dental organs ; the other kind 

 or the secondary, in the two genera, resemble each other just 

 as closely as do the primary ; and it is interesting to find that 

 these secondary teeth agree pretty closely with some of those 

 included in the genus Petalodus of authors, only they are oblique. 



In Janassa the association of these Petalodontoid teeth with 

 the primary ones is too obvious to be called in question. In 

 this form the two kinds are actually found arranged in order 

 side by side. This is proved by the specimens already referred 

 to and by Miinster's excellent figures. The Petalodontoid form 

 has likeAvise been obtained associated on the same slab with the 

 primary teeth of CJiinaxodus. We have in our possession a 

 small slab, not so large as the palm of the hand, on which there 

 are seven primary teeth, three or four of which lie in their na- 

 tural position. On this slab there arc likewise three of the Peta- 

 lodontoid form, two being in contact with the primary teeth, 

 and apparently not far removed from their original position. 



