Need ID

[jeff]

Found at Myrtle Beach.  Dark grey to black rock (about 12 cm X 8 cm) with round divots.  The divots are about 1 cm wide and 1 cm deep (pretty uniform).  Some have small clamshells in them.  I'm not a collector but I like shells.  Does anyone know what this is?  Did the clams cause the divots?  What kind of rock might this be? Any help would be greatly appreciated.  I could not find anything like this in Peterson's Field Guide.
Thanks, Jeff Gardiner

[dave r]

We really need a photo. What do you mean by 'divots'? Several species of Bivalve do actually bore into rock but without photos I could not say which species.
Dave

[paul monfils]

The commonest rock-boring clam in your vicinity is Rupellaria typicum, which I believe is included in the Peterson guide.  If you can extract one of the clams from the hole without breaking it, compare it to the picture.  If it is that species, the ones you described would be young ones.  It grows to about three times that size.  You could also check out Petricola pholadiformis.  Most of the other boring clams would usually occur either pretty far north or pretty far south of you.  Are you sure the matrix is rock, and not a thick piece of a large shell?  Such material often gets blackened after being buried in muddy sediment for a while.

[jeff]

Thanks.  I'll try to post a photo and I'll look at the shells closer

[jeff]

The divots look like someone stuck their thumb into a piece of clay to a depth of about 1 cm or so.   I'm a high school Chemistry teacher so I'm a little out of my element. One of the teachers in my building brought this back from spring break.
-Jeff