The Lined Top Shell (Phorcus lineatus), commonly called the lined or toothed top shell, is a small marine snail in the family Trochidae. Its solid, globose‑conic shell ranges from 10 mm to 35 mm in height and breadth, with six to seven convex whorls and a short spire. The shell is typically dull greyish or greenish, densely covered in fine, wavy or zigzag purplish‑black lines, often showing an eroded orange apex in older individuals.

The Lined Top Shell lives on rocky shores of the eastern North Atlantic Ocean—from Morocco and Portugal northward to Ireland and Wales—primarily in the mid‑ to lower‑intertidal zone under boulders, among cobbles, seaweed, and in rock pools. It is a grazing herbivore, using its radula to scrape microalgae, diatoms, and biofilm from rock surfaces, helping to keep algal growth in check.

Although not commercially fished, its attractive shell is sometimes collected by enthusiasts, and the species also serves as a bioindicator of coastal metal contamination. Despite being common and widespread, localised over‑collecting or habitat disturbance can impact populations, so collectors are encouraged to take only a few specimens and practise sustainable harvesting.

This specimen was collected in Plymouth in 1899.