First discovered by Commandant Beau in the Marie-Galante Island, Guadeloupe in 1855, the legendary « Quoy's Slit Shell » was the first living pleurotomariid species formally exposed to science. The encounter of this species is among one of the most important landmarks in malacology and generated great excitement, as previously this important ancestral lineage of basal gastropods were considered long extinct; the finding of living species opened up wholly new possibilities in studying the evolution of gastropods. It was therefore selected as one of S. Peter Dance's 50 « Rare Shells » (1969). The first specimen (i.e., the holotype) was taken from a fisherman's pot set in deep-water, and it was inhabited by a hermit crab. This was closely followed by the exposure of Entemnotrochus adansonianus (Crosse & Fischer, 1861) and Mikadotrochus beyrichii (Hilgendorf, 1877), up until now some 30 living pleurotomariid species have been described. In fact, M. beyrichii was illustrated in the Japanese books such as « Kigai-zufu » (Kenkado Kimura, 1775) and « Mokuhachi-fu » (Sekiju Musashi, 1843) long before the detection of P. quoyanus, but these books was not known to scientists in the western world then. Today, P. quoyanus is known to have a rather wide distribution around the Caribbean Sea from Yucatan, Mexico to Virgin Islands to Venezuela. Furthermore there is one recognised subspecies, P. quoyanus insularis Okutani & Goto, 1985, described from the Bermuda Islands and has a much taller spire with more swollen whorls. Specimens with a similar form has since been found as far as Honduras, however. The name Perotrochus gemma Bayer, 1965 was previously considered to be a separate species but is now regarded as a gemmate form of P. quoyanus and thus a junior synonym of it. The shell is therefore rather variable in spire height and strength of surface sculpture (i.e., 'gemmation'), the colouration is also variable from rather pale to strongly flamed with reddish axial bands. It is a carnivorous grazer feeding mostly on sponges and usually inhabit hard substrates in deep water around -180-350m. Due to its deep habitat it is still a rare shell, especially live-collected in fine conditon; such shells are virtually only obtainable using deep-water submersibles as trawls rarely operate near the rocky walls it inhabit. Typical shell length around 45mm., extremely large specimens may exceed 60mm.