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The Coilopoceratidae include dominantly compressed involute ammonites that are either smooth or broadly ribbed and have a characteristic suture in which the bifid lateral lobe has the branch nearest the umbilicus in a more lowered position than that of the other. The family inhabited the warm waters of the Tethyan realm during part of middle Cretaceous time. Hoplitoides, Coilopoceras, and the new genus Herrickiceras represent the family in the Western Interior. Hoplitoides, the oldest member of the family, appeared suddenly in New Mexico in the middle Turonian subzone of Collignoniceras woollgari woollgari (Mantell). The few specimens collected have affinities with H. koeneni Solger and H. wohltmanni (von Koenen) from the middle Turonian of west Africa. A little above the subzone of C. woollgari woollgari in New Mexico are rocks containing the new species H. sandovalensis associated with Herrickiceras. Coilopoceras was derived from Hoplitoides by loss of the truncated venter. The sequence of Coilopoceras in the Western Interior is, from oldest to youngest, C. springeri Hyatt, C. colleti Hyatt, and C. inflatum, n. sp. These forms are associated with species of Prionocyclus of late middle and early late Turonian age. Herrickiceras, which appeared suddenly in New Mexico, may have had its origin in Donenriquoceras from the lower Turonian of Spain. The Coilopoceratidae in the Western Interior are almost confined to New Mexico. A few specimens have been found in southern Colorado, and one specimen was collected in central Wyoming. Elsewhere the family is widespread in a belt on both sides of the equator in Africa, India, southern Europe, northern South America, and Mexico.

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