The « Panamic Comb Venus » is an immediate standout among bivalves with two rows of long spines protruding from the posterior slope of each valve as it is very unusual for a non-spondylid bivalve to have long spines. Younger specimens tends to have longer, more intact spines; large specimens usually have most spines broken off. It is a locally common burrowing filter feeder living on sandy bottoms from intertidal to -5m depth, but due to its limited distribution specimens are uncomm.on on the shell trade market. Large specimens with good spines, especially, are quite rarely seen. In life it is buried with its long spines positioned upwards, possibly used as a defence against predators. Distributed in the Eastern Pacific Ocean from Mexico to Peru, it is very similar to its congeners H. dione (Linnaeus, 1758) and H. multispinosa (Sowerby II, 1851). Hysteroconcha dione tends to have shorter spines and is distrubuted only in the Western Atlantic Ocean, whereas H. multispinosa is also an Eastern Pacific species but has more prominent, erect ribs and more numerous spines. Typical shell length without spines about 40mm., extremely large specimens may exceed 65mm. and length including spines may exceed 90mm. It has long been placed in the genus Pitar, and is still often seen listed under that genus.