52 
DAVIS : FOSSIL FISH EEMAINS. 
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 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, progres- 
sively diminish in size ; while at the same time the number 
comprised in each row decreases. From the oblique and apparently 
spiral disposition of the rows of teeth, their symmetrical arrange- 
ment 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 fishes " 
(Odontography, page 51). A comparison of the two forms shews 
how small is the difference between them, both in the characters 
of the teeth and in the form of arrangement. The arrangement 
of the fossil is ahnost exactly similar to the appearance which 
would be presented by the teeth of Cestracion if they were spread 
out and compressed. The most striking difference between them 
lies in the more obtuse arrangement of the anterior portion of the 
jaw of Agassizodus. It may be naturally inferred that Agassizodus 
and the Orodonts generally, Hke the living Cestracion, fed on 
Molluscs and other animals which were protected by, or encased 
in hard shelly coverings, the arrangement of the flat crushing 
teeth admirably adapting them to break or crush the hard substan- 
ces in order to extract the animal. The size of the fossil Orodonts 
may be inferred from a comparison with the existing species. The 
Cestracion found off the the shores of Australia is two to three 
feet in length and the jaws from three to five inches, the jaws of 
Orodus ramosus were probably three feet in length, and this would 
give the length of the fish at about thirty feet, a truly formidable 
creature. 
The modern Cestracian is possessed of two defensive spines, 
