Homolid crabs (known as “porter crabs” or “carrier crabs” ) are long-legged, deep water crabs that get their common name from carrying sponges, corals, and even urchins on the back of their carapace using a special pair of legs, a behavior thought to be a defense or camouflage against predators. Their fossils have been rare from the West Coast. A new paper names describes a new genus of homolid crab (Cretalamoha) from the Pender Formation on Vancouver Island in British Columbia and a new species (Paromola roseburgensis) from the early Eocene Roseburg Formation in Oregon. Another fossil homolid crab named Homola vancouverensis was found in the Eocene Hoko River Formation of Washington State and described in 2001.
Torrey Nyborg and Alessandro Garassino (2017) New Occurrences of Fossil Homolidae from the Eastern Pacific. Boletín de la Sociedad Geológica Mexicana 69(1): 135 ‒ 148
http://boletinsgm.igeolcu.unam.mx/bsgm/vols/epoca04/6901/%286%29Nyborg.pdf