CESTRACIONTS. 51 



several antero-posterior rows, along the margin and inner surface of 

 both jaws ; but the rows are more oblique than in the sharks, 

 although less so than in certain rays, as J?Ama; and the teeth pre- 

 sent greater diversity both of form and size, than in any other 

 existing plagiostome. The teeth of the upper jaw are delineated in 

 fig. 2, PI. 11. 



The teeth at the anterior part of the jaws are the smallest ; 

 they present a transverse, sub-compressed, conical figure, with the 

 apex produced into a sharp point ; these points are worn away from 

 the used teeth at the anterior and outer parts of the jaw, but are 

 strongly marked in those which still lie below the margin. There are 

 six subvertical rows of these small cuspidate teeth on each side 

 of the jaw, together with a median row close to the symphyseal line ; 

 and from twelve to fourteen teeth in a row. Behind the cuspidate 

 teeth, the five consecutive rows of teeth progressively increase in all 

 their dimensions, but principally in their antero-posterior extent ; 

 the sharp-point is converted into a longitudinal ridge, traversing 

 a convex crushing surface ; and the ridge itself disappears in the 

 largest teeth. As the teeth increase in size, they diminish in num- 

 ber, in each row ; the series of the largest teeth includes from six to 

 seven in the upper, and from seven to eight in the lower jaw. 

 Behind this row, the teeth, although preserving their form as 

 crushing instruments, progressively diminish in size ; while at the 

 same time, the number composing each row decreases. From 

 the oblique and apparently spiral disposition of the rows of 

 teeth, their symmetrical arrangement on the opposite sides of the 

 jaw, and their graduated diversity of form, they constitute the most ele- 

 gant tesselated covering of the jaws which is to be met with in the 

 whole class of fishes. 



The modifications of the form of the teeth above described, 

 by which the anterior ones are adapted for seizing and retaining, 

 and the posterior for cracking and crushing alimentary substances, 

 we shall find to be frequently repeated with various modifica- 

 tions and under different conditions in the osseous fishes. They 

 indicate, in the present species, a diet of a lower - organized character 

 than in the true sharks, and a corresponding difference of habit and 



E 2 



