346 MESSES. HANCOCK AND HOWSE 



teetli. They are more inequilateral and oblique than the smaller 

 primaries, one side being much more arched than the other. 

 The cutting-margin is slightly arched and denticulated, but is 

 narrow and only a little concave ; the crushing-disk, too, is wider 

 than long, the transverse imbricated ridges being reduced to 

 about half a dozen. 



The upper surface of all the teeth, whether primary or second- 

 ary, is covered with a thick layer of opaque white enamel-like 

 matter. This has a very striking appearance, contrasting as 

 it does with the dark hue of the rest of the tooth, and being 

 strongly defined around the margin by a thickened rim, which 

 is best seen when the tooth is turned with its face downwards. 



And, moreover, when the enamelled surface is a little worn, 

 it becomes pitted and freckled all over with dark irregular points, 

 which are sometimes elongated, particularly on the anterior or 

 cutting-margin. 



There is little difSculty in determining the manner in which 

 these curious teeth are placed in, or rather on, the jaws ; for 

 apparently the whole of the teeth of both jaws have been found 

 lying in their original position, though the jaws themselves have 

 entirely disappeared, they having undoubtedly been composed 

 of cartilage. Having carefully examined Mr. Duff's specimens, 

 which will shortly be described, and after a full consideration of 

 Count Miinster's figures and descriptions, we can have little 

 hesitation in giving the following account of the arrangement of 

 these rather extraordinary dental organs — and this notwithstand- 

 ing that we are acquainted with nothing exactly like it, either 

 in fossil or recent fishes, except in the so-called CUmaxodus. 



First, then, the teeth are arranged in both upper and lower 

 jaws (PI. X., figs. 2, 3) in precisely the same order. In both 

 they are placed in transverse horizontal rows, across the ante- 

 rior portion of the jaws, and in such a manner that never more 

 than a single row in each jaw is in operation at the same time. 

 Each such horizontal row is composed of seven teeth (five pri- 

 mary, two secondary), placed lengthwise, with the cutting-mar- 

 gin in front. A large symmetrical primary tooth is situated on 



