Fig. 3F
Natica impervia Philippi, 1845a: 65; Philippi, 1845b: 42, pl. 33, fig. 6; Melvill & Standen, 1912: 122 Tectonatica impervia — Dell, 1990: 163, figs. 249, 274 (synonymy and radula); Pastorino, 2005b: 231, figs. 36–45 (synonymy and radula)
Examined material. 4 sh. (MACN-In 40671)
Description. Shell height to 11.3 mm (up to 18.1 mm according to Dell 1990); ovate, solid. Protoconch of about 1 whorl; transition to teleoconch poorly defined. Teleoconch of up to 3.25 whorls, almost straight in outline; last whorl enlarged, very inflated, comprising about 95% of total shell height. Suture impressed. Surface whitish; only sculptured with faint growth lines. Aperture elongate-ovate, interior white; columellar callus strongly thickened, expanded, partially or fully covering the umbilicus.