Lima wacoensis is a pelecypod found in the Lower Cretaceous aged (Albian stage, 105-108 mya) Goodland Fm. of Tarrant county, Texas. It is ornamented with ribs that radiate from the umbo (beak like portion at the back of a pelecypod shell) and has very fine, concentric growth lines.
I purchased this fossil from Dan Woehr who seems to know every fossil exposure in Texas! Check out his collecting reports at The Meanderings of a Texas Fossil Hunter site which is a part of the Brazosport Museum of Natural History's Web site. While he won't give out the locations he hunts, he does a decent write up of what he finds and has loads of pictures.