Madagasikara johnsoni was originally discovered and described (under the name
Melanatria johnsoni) by
Edgar Albert Smith in 1882. The
shell is large, elongate-pyramidal, turreted, thick, covered with an olive epidermis. It is closely lineated or strigate with longitudinal lines of a darker tint. The shell has nine
whorls. Whorls are very slightly convex beneath, strongly spirally ribbed and grooved. The ribs are six in number on the upper whorls and rounded; the two above are much more slender than the four beneath; the uppermost borders the suture; the next lies in the concavity at the top of the whorls; and the rest surround the slight convexity, and are three times as broad as the sulci separating them. All the whorls, with the exception of the last four, are coronated at the slight angle below the excavation with very short, hollow, oblique spinules. Some of the spiral grooves exhibit rows of fine granules. The
last whorl descends somewhat, giving the shell a slightly distorted appearance. It is girded with about twelve transverse costae, a few at the base being smaller than five principal ones around the middle. The
aperture is bluish within, faintly stained with olive-brown near the margins. The peristome widely and deeply sinuated on the outer lip in the concavity of the whorl, arcuate and prominent in the middle, then shallowly sinuated again. Columellar margin is thickened, free, arcuate, reflexed, ending in a distinct basal sinus. The width of the shell is 24–28.9 mm. The height of the shell is 69.9-77.7 mm. The width of the aperture is 14.0-14.2 mm. The height of the aperture is 20.5-21.0 mm. There is not known description of
operculum. There is also not known anatomy of this species. Reproduction strategy is also unknown. ==References==