TABLE 1. Distribution and main characters of Leptochiton lignatilis n. sp., L. alveolus (M. Sars in Lovén, 1846) and L. belknapi Dall, 1878 , allowing comparisons.

Distribution/taxonomic characters Leptochiton lignatilis n. sp. L. alveolus L. belknapi
Stratigraphy Miocene of Italy Pliocene of Italy -
Biogeography - Atlantic Ocean Pacific and Indian Oceans
Valves Thinner and fragile Thinner and fragile Thicker and sturdy
Tegmental granules Irregular, rounded-subquadrangular shape More regular, smaller and closely packed, rounded-oval shape Larger and more widely spaced, oval to diamond-like in shape
Intermediate valves (IV) Rectangular Rectangular Rectangular
IV back Carinated Arched Carinated
IV anterior margin Almost straight Concave in the jugal area Almost straight
IV posterior margin Almost straight, apex not distinct Almost straight, apex obsolete or poorly marked Almost straight, obsolete or poorly marked
IV lateral areas Not raised Not raised Little raised, distinctly marked by a diagonal depression
IV height/width ratio 0.50 - 0.36
Tail valve (TV) More than semicircular Semicircular Semicircular to roughly triangular
TV anterior margin Convex Almost straight Convex
TV mucro Anterior Central Subcentral