<p><strong>Abstract.</strong> Three stratigraphically successive species of <i>Bradleya</i> Hornibrook, 1952 from abyssal sediments of the central equatorial Pacific (Leg 85, Deep Sea Drilling Project) form an unbranching evolutionary sequence designated as the <i>B. johnsoni</i> Benson lineage. These taxa are <i>B.</i> sp. 1 (Lower Oligocene), <i>B. johnsoni</i> (Upper Oligocene – Middle Miocene) and <i>B. thomasi</i> n. sp. (Upper Miocene – Recent). A shared synapomorphic character, the

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... ior bridge complex, establishes the kinship of these species. Their stratigraphic ranges and a traceable series of changes in the organisation and mass of the reticulum are consistent with the hypothesis of direct ancestor/descendant relationships between them. <i>Bradleya johnsoni</i> is distinguished from <i>B.</i> sp. 1 by the appearance of new primary muri in the posteroventral region and by a general increase in reticular mass. In <i>B. thomasi,</i> the overall reticular pattern is maintained but it becomes more delicate and less rectilinear. Each species of this lineage shows similar variation in the posteroventral reticulum.</p>