Diagnosis: Shell rather small, pale to whitish, with paucispiral protoconch. Axial ribs low and narrow, overrun by the spirals. Columella parallel to shell axis, three columellar folds, abapical one the weakest. Umbilical slit covered by callus.
Description: Shell slender, up to 19.8 x 12.5 mm (HD 16203-1), rather thin, especially in juveniles. Protoconch paucispiral, with 1-1,25 smooth whorls. Nucleus relatively large (d 0.3 mm), largest diameter 0.9-1.0 mm, exposed height 0.8-1.1 mm. In some shells the suture between protoconch and teleoconch is well marked, making the protoconch quite conspicuous. Transition to teleoconch poorly marked by a thin line or by the first axial rib of the teleoconch . Teleoconch with up to 4,75 whorls. Height of last whorl 75 % of total shell height in the larger shells. Axial ribs with triangular cross-section, rounded tops narrower than the spaces between them. Number of axial ribs: 8-10, 9-12, 9-12, and 10-12 on first to fourth whorl respectively. Spiral sculpture only consists of weak spiral lines between the axials and small rounded knobs on the intersections with the axial ribs. Number of spirals: 3-4, 3-4, 3-7, 5-7 on first to fourth teleoconch whorl, and 12-21 on the last whorl. The sutural shelf is distinct, but not very wide and sculptured with thin growth lines. Starting from the top of the axial ribs, a sharp lamella obliquely crosses the sutural plane: the lamellae are sharp on the top, and thicker at their base. Aperture elliptical, truncated posteriorly, with one tooth in the middle of the truncated part. Outer lip can have 8-10 lirae. Columella straight, parallel to shell axis, with three columellar folds: adapical one the strongest, middle one medium, and abapical fold medium to weak. Columellar callus thin, white, partly covering the umbilical slit. Most of the shells are whitish, sometimes with traces of pale brown, with a vague broad white spiral band on the last whorl.

In the Indian Ocean, only few species of the genus Scalptia with a paucispiral protoconch are known: e. g. S. androyensis Verhecken & Bozzetti, 2006, and S. contabulata (Sowerby (I), 1832). Scalptia androyensis is easily distinguishable by its very fine spiral striae and its low, broadly rounded axial ribs. Some shells of S. contabulata from Madagascar-Mozambique have unusually strong and narrowly spaced axial ribs, e.g. AVI 544-1. Such shells are easily differentiated from S. harmulensis by their lower spire, sloping-out sutural ramp, wider umbilicus, and only minor knobs on top of the axials ribs.
Scalptia harmulensis may also be confused with three other Scalptia species recorded from the Arabian Sea, viz. S. scalariformis (Lamarck, 1822), S. costifera (Sowerby, 1833) and S. scalarina (Lamarck, 1822). These names have been inconsistently used in literature; they are discussed below.
Scalptia scalariformis has a multispiral protoconch by which it is easily distinguished from the paucispiral protoconch of S. harmulensis. Moreover, S. scalariformis has fewer and smoother axial ribs than S. harmulensis. These axial ribs are stronger, straighter and more parallel to the shell axis in S. scalariformis, and the spiral sculpture is much fainter than in S. harmulensis.
Scalptia scalarina has fewer axial ribs, a much more solid shell, and a more open and deeper umbilicus than S. harmulensis. According to Lamarck (1822: 113), who was blind when he described the species, the shell surface is completely smooth ("n'a rien de rude au toucher"); but the lectotype does have fine close-set spiral lines on the last whorl (see also Kiener, 1841: 9). Compared to S. harmulensis, S. scalarina has a heavier shell with broad rounded axial ribs and a very fine spiral sculpture; its umbilicus is very deep (Kiener, 1841: 9).

Type locality: Harmul (24°3r39"N, 56°35'49"E), Al Liwa, in the northern part of the Oman coastline, Gulf of Oman, sandy beach.
Distribution: This species is known from off Oman, the United Arab Emirates, Dubai and Ras Hafun, Somalia.