ther than length of shell provides for the
lesser error from warping. There appears to be no close correlation of
proportions with either size or sex.

It is of interest that _Amyda ferox_ is the most distinctive in
proportions of the carapace. Its carapace is longer in relation to its
width than that of any of the other species. The average relative length
of the carapace of _A. emoryi_ is intermediate between that of _A.
ferox_ and the averages of _A. spinifera_ and _A. mutica_, but the
overlap in range with the latter two is complete.

The cause for kyphotic anomalies is unknown. That it is accompanied by a
greater degree of growth in the vertebral column than in the periphery
of the costal plates is obvious. There seems to be no well-established
accommodation for the difference in growth, since the hump produced by
it varies considerably in form.

There is no trend from small to large specimens in size of the hump;
large and small humps occur in both large and small specimens.
Accordingly it seems that the humped condition is developed in the late
embryo or early post-embryonic life, and does not later change.

An apparently reasonable hypothesis is that the costal plates ankylose
distally with the ribs early enough in embryonic life so that any
differential in growth rate between them and the vertebral column is
translated into abnormal contortions of the body. Agassiz and others
have shown that the costal plates normally do not fuse with the ribs by
the time of hatching; the fusion then does not normally occur in the
embryonic stage. Presumably, once fused, the costal plates and vertebral
column normally have equal growth rates, since the height/width ratio
does not change significantly with increased size. It is well known that
fusion takes place in young specimens soon after hatching; in all
skeletons examined of this genus, from the smallest (62 mm. in length)
to the largest (295 mm.), the fusion has occurred. Therefore, the normal
time of fusion must be approximately at the time of hatching.

Although costal plates and the vertebral column grow in direct
proportion to each other throughout life from a period shortly after
hatching, the vertebral column apparently grows more rapidly than the
costals shortly before and possibly also shortly after hatching, at
least in kyphotic and probably also in normal specimens. An
exceptionally early date of fusion of costal plates and ribs would thus
result in a kyphot