« Testa exilissima, orbiculata, depressa, superne subplanata, valde umbilicata, alba, nitida. Anfractibus 3, teretibus; ultimo longitudinaliter costato, transversim cinguiato. Apertura orbiculari. Peristomate continuo, distincto. » – Op. cit. p.12.
« All the whorls are nicely striated by growth-lines. The last one is adorned with 3 belts; one of them is dorsally placed, an other one is situated a little below the periphery, and the last one, which is the larger, encircles the umbilicus at the middle of the base. About 15 costae, progressively decreasing anteriorly, bear nodosities at their intersections with the spiral belts. On the other whorls, the costae and the spirals vanish. »

The shell differs from that of exilissima Philippi by its stronger sculpture, « especially the axial ribs » (Warén, about jeffreysii). But as both species are quite variable in sculpture strength, (« small specimens cannot be assigned to one species or to the other » – Nofroni & Renda), S. formosissima could be considered as « an extreme form, with massive and arched transverse ribs » of jeffreysii. This hypothesis remains to be confirmed (2022).