Oyster inside an oyster?

[pambosk]

Hello, I have a lot of oyster halves, maybe 60-80 and way too many fragments, however I haven't the single clue how they would look as a whole. There seem to be 5 categories of halves: the "half mango" (usually very big and thick), "the rippled shallow plate" (usually thin, but many layers), the symmetrical ones with even left and right sides (usually half the size from the previous), the round fist like ones with curved ending, and the stretched ones.  

 

Below I'm showing one, which a) has some interesting attach-marks and b ) even tho it is a "half mango style" inside it appears to have a "rippled shallow plate, which is smaller, and does not have the same attach marks.  It is also not so well preserved.  

 

Is this accidental? Are those two types the usual two valves of a bivalve?

 

Any help is very appreciated thanks. 

 

 

below the most accurate look of the marks, they look and feel like a row of teeth of sorts

 

and the inside oyster

 

location of most of the oyster finds (in relation to the sea) its about 5km 

[abyssunder]

The "inside oyster" is the upper valve of the oyster. You have both valves there still attached.

 

comparative images from here

[pambosk]

Ok this is a very helpful link thanks! However those fossils are dated Cretaceous, and my location is registered as: 

 

 

Is it possible??

If possible it means I have various kinds of:

Pycnodonte, Pelecypoda (above)

as well as various kinds of:

Exogyra, Pelecypoda (older post)

and many others that we will examine later

 

[abyssunder]

Both are in the same family Gryphaeidae. Exogyra disappeared in the Late Cretaceous, while Pycnodonte has a large temporal range (Creatceous-Pleistocene), so It could fit your fossil oysters, also there might be various species of the genus, some of them assigned to other genera, also in oysters the shape variability is common, making the things to be more complicated.

[pambosk]

just a taste of what I mean, those are not even half of my oyster finds.. however only 5 are complete with both their sides, beyond doubt, I will make a post on the one which is the best preserved.  Also a post on hanging markings and various epiobonts later. you can follow me if u are an oyster researcher.