Hi Nancy,
Cowries do most of their growing in the bulla stage.  Once the lip turns in
and the apertural teeth form, the shell doesn't increase much more in
overall length.  Therefore - the late bulla stage of a cowrie is nearly as
long as the final adult size of the shell.  A tiger cowrie that will be 80
mm in length when fully grown would be in the bulla stage (I estimate) until
about 70 mm in length.  I have seen a Cypraea cervus bulla, with a thin,
undeveloped lip, over 120 mm in length.  Once the teeth form, the shell
looks essentially like the adult, but you can tell a subadult cowrie because
it is much thinner and lighter in weight than the adult.  Because the bulla
stage is so thin, it is easily damaged by forces that would not damage an
adult cowrie.  Therefore bulla stage shells frequently have major growth
mends.  In many species the bulla is also different in color and/or pattern
from the adult.  For example, Cypraea cervus and C. cervinetta, which are
white-spotted as adults, are transversely banded in the bulla stage, with no
sign of the adult pattern. C. tigris however, as you observed, develops its
adult pattern quite early, in the late bulla stage.
Paul M.