The Miocene and Pliocene faunas of the West Indies and Central America should be compared only with European faunas that lived under essentially similar conditions. These American faunas, with the exception of a supplementary Mexican fauna, are almost purely tropical, according to the distribution of their living genera. The Miocene and Pliocene faunas of the Mediterranean region and the Miocene faunas of Aquitaine, which most closely resemble these American faunas, include the following temperate genera:2Mytilus (Mytilus), Astarte, Cardium (Cerastoderma), Macoma (Macoma), Solen (Sole'n), Ensis, Saxicava, and Aporrhais. None of these genera are in any of the West Indian Tertiary or living shallow-water faunas. All except Aporrhais are common in the Tertiary and living faunas of the Atlantic coast of the United States. Aporrhais has not been found in the Tertiary faunas of the Atlantic States, but is living in temperate waters on both sides of the Atlantic. Although . . .