On the Fossil Fishes of the Carboniferous Limestone Series of Great Britain. 389 
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 number 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 
elegant tesselated covering of the jaws which is to be met with in the whole class 
of the fishes.” 
Comparing the above description of the still existent Cestracion and the Coal 
Measures Agassizodus, a striking simlarity is observed in general form and arrange- 
ment of the teeth on the jaws, as well as in the characteristics peculiar to the 
teeth individually. It is only in matters of detail, in the number of the teeth in 
each row, and the number of rows, that any striking difference is perceptible. The 
dentition of Cestracion is adapted to crush hard and resistent objects like the 
shells of the mulluscs, or the hard covering of crustaceans, and it is probable that 
the teeth of the Orodonts were used for the same purpose. 
Neither in American nor English strata have specimens been discovered which 
illustrate more than the arrangement of the teeth. Whether the fishes possessing 
them were possessed of defensive spines asin the case of the modern representative, 
is unknown. 
A comparison of the recent and fossil teeth will afford some idea of the great size 
of the Cestraciont fishes of the Carboniferous age. The living fish found in the 
Australian seas is two to three feet in length, and the jaws occupy about one-eight 
of that length. The jaw of one of the larger specimens of Orodus ramosus must 
have been at least three feet in length—if we may deduce the length of the jaw 
from the relative size of the teeth—and the jaws being one-eighth the length of the 
entire body, gives the latter at twenty-four feet. 
The following British genera appear to possess characters which associate them: 
in one group and they are, along with the American genus Agassizodus, here included 
in that of Orodontidze -— 
Orodus, Agassiz. 
Lophodus, Rowanowsky. 
Petrodus, M’Coy. 
Agassizodus, St. John and Worthen. 
Rhamphodus, Davis. 
Diclitodus, Davis 
