I'm not sure that "hybrid" is the right term to use for an intermediate form
between Cypraea annulus and Cypraea obvelata.  The two are very similar, and
some authors have even suggested that C. obvelata is just a heavily calloused
form of C. annulus.  I have seen various populations from rather diverse
localities, and there does seem to be quite a range of callous development.  I
have had some lots of C. annulus where the sides of the shell were unusually
distended, but not to the extent you would expect to see in C. obvelata.  I
have also received shells sent to me as C. obvelata which simply looked like
somewhat swollen C. annulus, while other C. obvelata are bizarre creatures
with callouses so pronounced that the dorsum of the shell is lower than the
callouses.  If I had a shell that appeared intermediate in callous formation
between typical C. annulus and typical C. obvelata, I don't think I would
assume it was the result of mating between the two extreme forms.  I have just
seen too many specimens, and sometimes entire lots of specimens, which I would
have to describe as intermediate.
Paul Monfils
Rhode Island, USA