Description: The shell is higher than wide, otherwise like that of Megalomphalus.
Remarks: The type species Macromphalus reticulatus S.V. Wood, 1842 from the Pliocene British Crag Formation has such a similar shell with the type to the living Couthouyia A. Adams, 1860 that Waren and Bouchet (1988, figs. 26, 27) consider them synonyms.

Macromphalus is just like Dialytostoma with exception of the last formed whorl of the adult shell that remains in contact with the spire, while it detaches from it in Dialytostoma. Macromphalus differs from Megalomphalus by a shell that is higher than wide and from Vanikoro by its inclined aperture, the wide umbilicus and the protoconch with very fine sculpture.

The genus Macromphalus was established by S. V. Wood (1842) with the monotypy Macromphalus reticulatus S. V. Wood, 1842. In the original description, this genus was defined by a fusiform shell with an elevated spire, an ovate aperture, a sharp outer lip and a linear umbilicus. For a long period the family rank of Macromphalus was uncertain and species in Macromphalus were commonly confused with Fossarus Philippi, 1841 (Cerithioidea: Planaxidae: Fossarinae) due to the globose shell shape, wide umbilicus and developed spiral ribs. Nevertheless, the two genera distinctly differ in anatomical features and Macromphalus should be placed in Vanikoridae as Waren A. & Bouchet P., 1988. discussed. The distributions of Macromphalus mainly includes western Pacific, Indian Ocean, eastern Atlantic and Mediterranean. Among type localities of formerly known extant Macromphalus species, one is in Hong Kong, China, three are in Japan and nine belong to southeast Asia sea areas.

Macromphalus differs from Fossarus in:
1) having a penis.
2) having a large fleshy epipodial flap on each side of the foot.
3) having tentacles that are round in cross section.
4) having a paucispiral operculum with lateral nucleus.
5) having oar-shaped marginal radular teeth.
6) having a foot that is divided in two sections, a posterior sucker-shaped one that presumably is used for attachement and an anterior motile part.
All these characters agree with Vanikoro, and we are not aware of any major differences in the soft parts between Vanikoro and Macromphalus. Therefore we find it justified to transfer Macromphalus to the Vanikoridae.
Megalomphalus and Talassia differ from Macromphalus in having a more normal foot, not divided so clearly into sections, but they have very similar epipodial folds and all other features observed agree with the Vanikoridae. We have therefore decided (as PONDER 1985 suggested for Talassia) to move them to Vanikoridae, where they can be regarded as less modified species.