Two marine fossils needing ID. Is this rudists and coral?

[Creek - Don]

I found these two in the Dallas area creeks today.   It was washed down from upstream lying with other creek rocks.  First one looks like coral and second one looks like rudists.   I will let someone ID this for me since I'm new to marine fossils. 

[JohnJ]

The smaller of the two is indeed a portion of a Durania rudist.  The larger may be tufa.

[Creek - Don]

Thanks JohnJ.  Never seen a Tufa rock before, but does seem to occur in limestone rocks.