A limited exposure of Upper Cretaceous marine siltstones and claystones near the coastal town of Carlsbad, southern California, contains a remarkably well preserved microfauna.

Twenty-six species of ostracodes including twenty-three new species and one new trachyleberid genus occur in the upper part of the section. This faunule possesses distinct Cenozoic affinities expressed by the presence of the genera Trachyleberis, Actinocythereis, and Idiocythere, all of which previously have been reported from rocks no older than Lower Tertiary. Generic affinities with European faunas are also noted by new species of Idiocythere, previously reported from the Eocene of Germany only, and Isocythereis, previously from the Cretaceous of Germany only. Three species occur which also occur in Upper Cretaceous rocks of the U. S. Gulf Coast. These are Brachycythere darensis Swain, 1952, Krithe cushmani Alexander, 1929, and Cytheropteron coryelli Schmidt, 1948.

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