Investigation of known Seguin localities led to the discovery of an overlooked diverse and abundant marine fauna in Solomon's Branch, a stream in Bastrop County, Texas. The fauna, a transported assemblage from a marine littoral environment, encompasses a mix of specimen types from large wave-worn individuals to the smallest unworn ornamented species. Following the discovery of this fauna, further field work was undertaken and other Seguin localities with different depositional environments were found and collections made from those sites. Finally, a further suite of specimens was examined within the Texas Natural Science Center, some from localities no longer in existence or now lost. The environment is transitional in character from the deeper water Midway to the nonmarine environment of the chiefly terrestrial Texas Wilcox deposits, and represents the last major marine transgression in this area prior to the Eocene.

The fauna is a mix of that derived from early Paleocene and Cretaceous taxa as well as elements that appear to originate from western Africa, the Tethyan region, and the western coast of America. The inferred species' habitat includes a near-shore open marine element, a probable lagoonal component, and brackish water elements. From the 115 molluscan taxa recognized, six have not been recognized to date in sediments later than the Cretaceous, and 30 represent from the Eocene or later records.