TESTUDINATA. 
51 
When we compare closely the xiphiplastron of the two species 
we find various differences which show themselves to the eye. The 
outer face of the wall running along the outer border of the bone 
is, at the anterior end, perpendicular in both species. Further 
backward, about one-third the distance to the extremity of the 
bone, the outer face of the wall in T. crassiscutata has become 
slightly convex fore-and-aft (pi. 8, fig. 8, a, a) and quite con¬ 
vex (pi. 8, fig. 8, c, c) from below to its upper border; where¬ 
as, in T. sellardsi it has become concave from front to rear (pi. 
8, fig. 8, b, b) and only slightly convex (pi. 8, fig. 8, d, d) 
up and down. 
From the summit of the wall mentioned its inner face falls 
off much more rapidly in T. crassiscutata than in T. sellardsi, so 
that at a distance of 80 mm. from the outer border of the bone, 
measured on the lower surface, the thickness is greater in the latter 
(40 mm.) than in the former species (35 mm.). At a point about 
halfway along the inner face of the wall the upper surface of the 
bone has sunken so much that a sort of wide pit is produced. In 
T. sellardsi this pit is much shallower. 
The upper surfaces of the lobes of the xiphiplastron which 
were covered with horn are disproportionately broader in T. crass¬ 
iscutata (85 mm.) than in T. sellardsi (65 mm.). The lower sur¬ 
face of the xiphiplastron of the type of T. crassiscutata is smooth; 
that of T. sellardsi are provided with vermiform grooves, from 3 
mm. to 5 mm. in width and of varying depth. These continue on 
the horn-covered parts of the upper surface. This feature may 
have been individual. 
The lack of common parts makes it practically impossible to 
compare the carapaces of the two species here mentioned. In the 
U. S. National Museum are two neural bones, found near Tampa, 
Florida, which the writer has figured (Foss. Turtles N. A., p. 
460, fig. 618). It is, however, not wholly certain that they be¬ 
longed to T. crassiscutata. One of these is the fourth neural and 
may, therefore, be compared with the fourth of T. sellardsi (pi. 
8, fig. 6). It will be seen that they differ somewhat in out¬ 
line; but this may not be important. The length of that of T. 
crassiscutata is 130 mm.; its width, 200 mm. The length is, there¬ 
fore .65 of the width. In T. sellardsi the length is .53 of the width. 
In both species the width of the third vertebral scute was about 
300 mm. 
