Thin sections of Paleozoic Ostracoda and their bearing on taxonomy and morphology

The study of thin sections of Paleozoic and Tertiary ostracodes reveals that some forms possess shells of many layers, in contrast to the one-layer of most fossil ostracodes. Both the genus Eridoconcha and the new genus Cryptophyllus exhibit a many-layered shell which appears to be formed by the retention of molts. It is proposed that the cohesion of these molts is not dependent on shape of the carapace but is a specialized adaptation of generic importance. The genera Eridoconcha and Cryptophyllus are included in the family Primitiidae. The genera Leperditia and Isochilina, in thin section, reveal a layer of shell internal to the primary layer which commonly is restricted to the dorsal and ventral margins of the valve. The significance of the secondary layer can not be definitely established at present.