FISHES OF THE CARBONIFEROUS SYSTEM. 191 
to them must have been capable of lacerating and destroying most of the 
inhabitants of the Carboniferous ocean. Sharks were the most abundant 
and the most powerful of the fishes in that sea, and to these Calosteus must 
have been a formidable antagonist. 
It will be noticed that the jaw described above has lost all of its teeth 
and it has apparently suffered long maceration. ‘The treatment to which it 
has been subjected may also have removed from it more than the large 
teeth, of which the sockets yet remain, viz, a tuberculated surface and a 
row of small teeth. Were these present it would come near to Lhizodus, 
but the jaw of a well-marked species of that genus recently discovered by 
Mr. McAdams in the same beds shows the exterior tuberculation, the row of 
small teeth along the upper margin, and the great laniary teeth still in posi- 
tion and deeply implanted in the massive dentary bone. 
RHIZODUS ANCEPS, 0. Sp. 
Plate XLIII, Fig. 1. 
Dentary bone one foot or more in length, massive and strong; exterior 
surface coarsely pitted and tubercled; upper margin set with numerous, 
closely crowded, conical, acute, robust, striated teeth about half an inch in 
height, and with three or more laniary compressed, ancipital, enameled, 
polished fangs, plicated at the base, two inches or more in height, by nearly 
an inch in breadth. These laniary teeth rise from a shoulder or shelf which 
runs along the inner side of the mandible, and are deeply rooted in its sub- 
stance The largest is set at or near the symphysis, where the mandible is 
tumid and very massive. This tooth is slightly curved, much compressed, 
with trenchant edges; the others are somewhat smaller, less compressed, 
and less curved. 
Only about ten inches of the anterior extremity of the right mandible 
of this fish is yet known. It was obtained by Mr. William McAdams from 
the Saint Louis limestone at Alton, Ill. It is considerably mutilated, but 
shows two laniary teeth in position and the impression of a third. The sec- 
ond is located four and a half inches behind the first, the third three inches 
behind the second. As the jaw is seen from the outside the total length of 
the laniary teeth is not shown, but the anterior one probably projected three 
