558 PROF. OWEN ON THE ENDOTHIODONT REPTILIA. 
are subequal. A small pulp-cavity, circular in transverse section, is 
exposed in each tooth, larger in the first than in the rest. The 
series deviates very slightly from a straight line. 
_ The second row (1-10') begins outside of and opposite to the in- 
terval between the cighth and ninth teeth of the inner row. Ten 
teeth are exposed, in section, in the second row, which extends 1 
inch 4 lines behind the last tooth of the inner row. There is a 
fragment of what seems to be a tooth anterior to the first of the 
second row, and which would indicate that this row included eleven 
teeth like the inner row. 
The foremost evidence of a tooth of the outer row (1*-6*) appears 
opposite the interval between the second and third of the middle 
row ; it is represented by the outer half of the shell of an incom- 
pletely calcified crown. It is succeeded by a similar evidence of the 
coronal shell of a second tooth. The third, opposite the interval 
between the fourth and fifth of the middle row, shows the circular 
wall of the crown almost complete. The fourth and fifth teeth are 
fragmentary. The sixth tooth outside the interval between the 
seventh and eighth teeth of the middle row shows the entire section 
of its crown with a less wide pulp-cavity; it had been cut across 
nearer the apex. A seventh tooth of the outer row is less satisfac- 
torily seen, and there are feeble indications of an eighth tooth. 
Three teeth in the same transverse line are thus shown, composed 
of the tenth and eleventh of the inner row, the third and fourth of 
the middle row, and the first and second of the outer row. ‘The best- 
shown teeth of the outer row have the same shape and nearly the 
same size as the others, but have wider pulp-cavities, which may 
indicate either that they have been cut across nearer their base or 
were less advanced in formation. 
The larger portion of mandible of Hndothiodon bathystoma here 
described and figured closely corresponds in size and shape with the 
similar portion originally described and figured (op. ct. pl. Ixvii. 
figs, 2-5). In both the apex of the symphysis has been broken off; 
but in the later-received specimen above described the thick alveolar 
border of the right dentary had undergone less damage and was con- 
sequently selected for the section figured. That of the left dentary, 
though more abraded, permits eleven teeth of the middle row to be 
traced, the series commencing a little in advance of that of the 
right side, unless the fragmentary indication of the foremost tooth 
of that side be rightly interpreted. 
The first, second, and third teeth of the middle row, left ramus, 
show, in section, a slightly incurved part of the periphery next the 
contiguous tooth of the inner row, such as one might see in asimilar 
transverse section of the deciduous and successional teeth in the 
alveoli of a crocodile ; but in such section the old tooth, the com- 
pleted crown of which was being pressed upon by the new tooth, 
shows a more solid structure with minor indications of a pulp-cavity. 
In the three foremost teeth of the second row of Endothiodon the 
pulp-cavity is as large as in the three hindmost teeth of the inner 
row, aud, moreover, the teeth of the middle row which follow and 
