Elasmostoma bajaensis n. sp., a pharetronid calcareous sponge, is described from the lower Eocene (P8 or P9 Zone) portion of the Bateque Formation, Baja California Sur, Mexico. This is the first Tertiary record of this genus and its first Western Hemisphere occurrence. Elasmostoma has been previously reported only from Jurassic and Cretaceous strata of Western Europe.

The clypeasteroid echinoid Astrodapsis bajasurensis n. sp. is described from upper middle Miocene beds of the Isidro Formation near the mouth of Arroyo Mezquital on the Pacific coast of north-central Baja California Sur, Mexico. The new species is the first occurrence of Astrodapsis outside of California and extends the southern limit of the genus by 1,100 km.

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The oligopygoid echinoidHaimea bajasurensisn. sp. is described from middle lower Eocene (”Capay Stage”) shallow-marine sandstones in the middle part of the Bateque Formation and shallow-marine limestones in the upper part of the Tepetate Formation, Baja California Sur, Mexico. The new species is both the earliest and the westernmost oligopygoid, and the first occurrence ofHaimeain North America.

The cassiduloid echinoid Calilampas californiensis n. gen. and sp. is described from middle lower Eocene (“Capay Stage”) shallow-marine sandstones in both the middle part of the Bateque Formation, Baja California Sur, Mexico, and the lower part of the Llajas Formation, southern California. The new genus is tentatively placed in family Pliolampadidae. The cassiduloid Cassidulus ellipticus Kew, 1920, previously known only from the “Capay Stage” in California, is also present in “Capay Stage” shallow-marine sandstones of the Bateque Formation.