Crab carapace?

[Sydney]

Unknown fossil. Found just below a tidal deposit and above a deep water lime deposit. In this layer there are a lot of good sized amonites, and a smattering of pelecypods and scallops and oysters and protocardia and urchins that become much more common just up the rock sequence. Just a bit deeper are fairly common trace fossils of burrowing shells.

 

 

[Rayminazzi]

Can we get closer pictures

[Zenmaster6]

Quality and size are okay.
I need a picture from the side though. I want to see from a different angle. 
My initial impression: It certainly looks crab like. The way the basal is flat is signature crab shape. It has a medium probability of being a crab but could also just be a suggestive rock.

[Sydney]

Hope these are better. Definitely is a fossil of some sort and not just a rock. 

[Sydney]

[Zenmaster6]

1 hour ago, Sydney said:

it lacks good markings to identify it to a species but I would agree that is a crab.
I am not a professional like some other people on here. Wait for their answers.

[Al Dente]

It looks like a brachiopod. I think Kingena is the common Cretaceous one from Texas.

[erose]

2 hours ago, Al Dente said:

It looks like a brachiopod. I think Kingena is the common Cretaceous one from Texas.

 

If indeed the Austin Chalk it would be too young for a Kingena, or at least any I know of. The central "line" and symmetry does suggest brachiopod. But it also appears to be just the interior cast of whatever it was and that makes for a mystery. So still wouldn't rule out a crab.

 

Cool fossil.

[Zenmaster6]

brachiopods and crabs still in the matrix amaze me at how similar they can look.