Middle Eocene exposures on the Brazos and Little Brazos Rivers yield numerous specimens of a wide variety of fossils, especially mollusks. Although this fauna has been known to paleontologists for many years, relatively few of the fossil groups have received a detailed analysis.

Eighteen species of scaphopods have been found in the Stone City and Cook Mountain (Claibornian) Formations of the Brazos River valley. These include 11 species of Cadulus, 4 of Dentalium, and 3 of Fustiaria. Of these, 10 species are new.

Apical fragments show that some scaphopods truncate their apexes by periodically discarding a significant portion of the test. By some mechanism or process, probably absorption, shell material is removed at a distance from the apex. The configuration of this shell removal is such that apical slits or grooves are already formed when truncation occurs. After truncation a pipe or sheath, which extends from the orifice of the truncated apex, may develop.

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