The ostracodes are small, bivalved, aquatic crustaceans which have the
external appearance of small clams (Pl. 34). The remains of these tiny
animals are so small that they are best studied under a low-power
microscope, and because of their small size they are particularly useful
to the micropaleontologist.
Fossil ostracodes range from Ordovician to Recent in age and have been
recorded in the Paleozoic, Mesozoic, and Cenozoic rocks of Texas. Their
remains are particularly abundant in certain of the Cretaceous and
Tertiary marine formations of the State.