Dakshinavarti shankha (), also referred to as Valampuri shankhu () and Sri Lakshmi shankha () is a sacred Hindu conch. It refers to the shell of a large sea snail from the Indian Ocean (a shell of the species Turbinella pyrum), but one that has a rare reverse-turning spiral. The shankha is held with the spout (siphonal canal) pointed up; its spiral twists rightwards rather than the more common form, which twists leftwards. Terminology In scientific usage a dextral (, right) shell has the opening on the right, when viewed with the spire . The opposite is sinistral (, left). This is consistent with the terms for right-handed screws in engineering and physics. Most species of sea snail are dextral. Within a typically-dextral species, rare individuals may develop sinistral coiling. In religious usage, the (sacred conch shell) is displayed spire . In this orientation, a common dextral shell has its opening on the left (). It is rendered in Sanskrit, in Hindi, and shankhu in Tamil. Authenticity The true Lakshmi shankha is a rare sinistral Turbinella conch shell from the Indian Ocean, usually from Turbinella pyrum. Other right-turning sea snail shells are often mistakenly sold and worshiped in place of the genuine shankha. One common substitution is the lightning whelk (Sinistrofulgur perversum, previously named Busycon perversum) from the Atlantic coast of North America. The real shankha has 3 to 7 ridges or plaits on its columella, whereas whelk shells have no such plaits. The so-called "flower-bud opening test", and the "rice pulling test" (Valampuri said to rise up through a rice heap) are non scientific. The best authenticity test is to take an X-ray image of the Valampuri. Valampuries show some morphological variation depending on origin, and shells with mixed characters of two adjacent localities are seen. In South India, people trust only the Rameshwaram type of Valampuries, and do not trust other varieties from the West Coast and Bay of Bengal, though these are also true Valampuries. In South India, people specifically worship 'Gauri Valampuri'. This Valampuri shows small dark spots on its body whorl, near the conch cavity. These dots are of conch skin i.e. of periostrachum in the form of small dark coloured pustules firmly attached in very small ditch or cavities, and difficult to remove. In case such periostrachum pustules are removed, dark coloured spots still appear on the conch body. The Gauri Type (with periostrachum