Shell oval globose, with the apex not prominent, white, fairly solid and not translucent. Protoconch with 1,125 whorls. The nucleus has a diameter of 0.09 mm, with a microscopically roughened surface, that extends for a little more than a half whorl. This sculpture is then replaced by several fine spiral threads, very irregular and more nume¬rous than usual (about 14), which are more irregular near the end of the protoconch and are fused with other nearby extensions. Colour white. Teleoconch. The holotype has 2,25 whorls with rapid development; it is sculptured with elevated axial ribs which are crossed by many small spiral threads; the axial ribs number 34 on the first whorl, later disappearing on the body whorl, where they are replaced by very numerous crowded lines. Aperture ovoid, wide, with the outer lip a little sharp. 18 prominent ribs extend into the wide umbilicus.

The morphology of the shell and protoconch is enough to consider the species in the genus Macromphalina. The species with the most similar shell is M. redferni, but the protoconch of this last species is brown and the spiral lines in the protoconch more regular, finer and without supplementary connections between them. M. diazmertanoi has its protoconch with a different sculpture, the threads fewer and with only axial extensions. Another species with irregular spiral threads on the protoconch is M. jibacoa, which is differently sculptured, with many tubercles and it has the supplementary lines in a spiral direction.

Only known from Tobago.