Day—On Acrodus. 59 
palate of Acrodus Anningie and in a pair of dorsal spines, asso- 
ciated with teeth, of another individual of the same species. 
The palate (Pl. ILI.) consists of an almost complete series of 
teeth, retaining the position that they must have occupied upon 
the jaw during life. ‘The bone upon which they were based 
has altogether disappeared; this fact and the absence of spines 
or any other remains anywhere near where the specimen was 
found, suggest the probability of its belonging to a detached 
lower jaw, “of which the car tilaginous structures have perished. 
Counting from either extremity of the series to the middle, we 
have on each side eight transverse rows of teeth, with a central 
row resting where the symphysis, or line of junction, of the 
jaw-bone would have been. ‘Two very small displaced teeth 
at the right extremity seem to indicate that there were origi- 
nally nine rows upon each side. ‘The two sides are not quite 
symmetrical, the right-hand series appearing more flattened and 
expanded than the left; and it is probably owing to this distor- 
tion that fewer teeth are discoverable in each row (excepting 
two) of the latter than in the corresponding ones of the former. 
Commencing from the extremities of the series, the first row 
on the right side is indicated by the two small teeth above- 
mentioned: all trace of this row is wanting on the left. 
The second row on the right contains 4 teeth;* ditto on the left 4 teeth 
”? third bP) 9 6 9 ”? 6 br) 
” fourth 23 te) vi 2? ? 2? 
”? fifth 9 ” 8 29 2? 6 72 
” sixth ” ”? 8 oP) ”? 6 2”? 
? seventh 2? ” 7 ”? ” 6 +B) 
” eighth ted bed 6 t ? ? i) ” 
ninth _ Gitar. “ Dyaee: 
And the central TOW contains 5 
Looking at the characters of the various teeth, thus grouped 
together, one at first feels doubtful whether the specimen 
should not be assigned to a Hybodus rather than to an Acrodus ; 
for, although the teeth of the posterior rows are marked with 
the fine strie characteristic of the latter genus, and are of a 
more or less depressed form, yet they all show some tendency to 
develop slight elevations, towards the apices of which the lines 
of enamel converge. In the more forward teeth we find, in the 
seventh row, the median elevations becoming more distinctly 
conical, and the ridges of enamel, which converge upon them, 
becoming coarser and more widely separated ; and in the eighth, 
ninth, and central rows these characters are so strongly brought 
* One of these is displaced to the outside of the third row. 
{+ The single detached tooth outside these appears to belong to the central row. 
+ The sixth tooth of this row is scarcely visible. 
