Fossil decapod crustaceans from the lower Tertiary of the Prince William Sound Region, Gulf of Alaska

Abstract

Sixty-five fossil brachyuran crabs, collected from rocks of the Orca Group, Tokun Formation, and Poul Creek Formation, have been assigned to six species, five of which were described previously. One of these, Pilumnoplax hannibalanus, is reassigned to Neopilumnoplax. Morphologic descriptions of Raninoides vaderensis, Eumorphocorystes naselensis, Portunites alaskensis, and Branchioplax washingtoniana are emended. Orbitoplax plafkeri n. gen. and sp. is described from the Poul Creek Formation on Wingham Island. The diagnosis of age for the Orca Group has been problematic. However, the well-preserved brachyurans, Branchioplax washingtoniana, Neopilumnoplax hannibalanus, and Raninoides vaderensis, provide corroborative evidence for an Eocene or older age for the rocks. Alaskan decapods include species common to the entire Pacific coast north of California, as well as species endemic to Alaska.