VARIOUS SPECIES OF CTENODUS. 65 



the denticle and ridges are coated with enamel, and shine very 

 brilliantly. 



There are sixteen specimens of this minute species in our col- 

 lection ; they were obtained at Newsham and Cramlington. 



The mandibular tooth is very similar to the upper one, but is 

 a little narrower ; the latter is somewhat more than half the 

 length of the maxillary bone, the posterior extremity of which is 

 not much enlarged, and is diagonally truncated. 



This is the tooth before alluded to as having been found in 

 connexion with the head of the entire fish, of which a general 

 description has already been given. It is therefore unnecessary 

 to say more respecting it on the present occasion. 



6. Ctenodus imbkicatus, n. sp. 



Tooth depressed, very thick, hollowed or slightly concave, 2J 

 inches long and upwards of an inch broad, with the inner mar- 

 gin well and regularly arched, the anterior slope being much 

 longer than the posterior ; the outer margin is nearly straight, 

 but on account of the projection of the surface -ridges is coarsely 

 denticulated ; there are six of these ridges or plaits ; they en- 

 large rapidly towards the outer margin ; they are strong, smooth, 

 and somewhat distant from each other, and, though mostly in- 

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

 an imbricated appearance ; the grooves dividing the ridges are 

 angulated ; the surface is minutely granulated, and the edges are 

 enamelled. The mandibular tooth is very narrow and fusiform ; 

 the ridges are not imbricated, and the grooves are scarcely angu- 

 lated. 



This species is not common : we have found only six or seven 

 specimens of it ; they were all obtained at Newsham. Two of 

 these, an upper and a lower, are large and in an excellent state 

 of preservation ; the others are quite small, but, like the large 

 ones, have six ridges, and agree with them in every particular. 



This, and the following species, have some resemblance to 



