Linda,

First, it would be nice to know where you collected them.  However, if all
were found in the same locale and the adult has ridges over the entire
shell, you probably are collecting M. campechiensis (Gmelin, 1791).  M.
mercenaria has a smooth center in the large shells.  M. m also frequently
has purple on the interior, but very rarely so for M. c.  There was a named
form (notata Say) that has a brown zigzag pattern on the exterior, which can
be sparse or cover almost all the shell.  In my experience the pattern
persists in the adult shell.  I've found that for both the ridges are more
pronounced in the juveniles.

V. rigida would be a very rare find in Florida (Abbott restricts it to the
Keys).  If all those you found were from the SE coast and have color pattern
on the exterior, consider Puberella (Chione) intapurpurea (Conrad, 1849).

Marlo


-----Original Message-----
From: Conchologists of America List
Behalf Of Linda Bush

Hi, Gang!

Can someone please describe a juvenile Mercenaria mercenaria for me?   I
have been having trouble with small shells (say, perhaps the lagest of which
would be an inch and
three quarters in length), which are very similar to the mercenaria shell,
but the ridges are much more pronounced, and many of them have a colored
pattern.   Could this be the shell that loses the color and ridges as it
gets bigger (although I have one which is much bigger than the
aforementioned "babies," which retains both the pattern and ridges.

Otherwise, the shells are almost identical, i.e., the hinge, the palial
simus, the escutcheon, and the lunule.

I had previously identified some of these as Ventricolia rigidia
(I think), but am really wondering if I am not look at young Mercearias.

Confused by the Venerid clams,
Linda