Penion is a genus of large marine snails, commonly known as siphon whelks, classified within the mollusc family Austrosiphonidae, the true whelks.
Penion species are restricted to the Southern Hemisphere. Two extant species are currently classified in waters surrounding Australia and five extant species are documented from New Zealand.
Numerous fossil species are recorded in New Zealand, Australia, Argentina and Chile, and Antarctica. In New Zealand, many fossils are found in Wanganui Basin sediments.
During the voyage of HMS Beagle, fossils of P. subrectus were among palaeontological samples collected by Charles Darwin from the mouth of the Santa Cruz River in Argentina.