Neoguraleus amoenus is a species of sea snail, a marine gastropod mollusc in the family Mangeliidae.

H. Suter in his "Manual of New Zealand Mollusca" (1913) had no doubt that Mangilia protensa and Pleurotoma (Drillia) amoena are one and the same species.

The following is the description given by H. Suter for Mangilia protensa: The shell is fusiform, elongated, turreted, thin and fragile.

The sculpture consists of subequidistant fine axial riblets, obsolete on the shoulder and below the periphery of the body whorl, 15 to 20 on the body-whorl.

The outer lip is thin, sometimes strengthened by the last axial riblet, with a shallow rounded infrasutural sinus.