Shell moderate to high, without distinct shoulder; base flattened; sculpture of numerous fine spiral lirae and very fine axial growth-lines giving a lustreless finish; aperture roundly three-cornered. Variably patterned with shades of brown. Description: Shell moderate to high (L/D = 0,67-0,85), cyrtoconoid; whorls rounded but not evenly so, curvature sharpest just below suture and at periphery but not forming sharp angulations; periphery below mid-whorl; distinct shoulder absent, suture sometimes slightly sunken; base flattened; teleoconch of up to 3,5 whorls. Sculpture primarily of numerous close set spiral lirae, 1-3 times the width of their intervals; those bordering umbilicus stronger and broader; sometimes obsolete on base between umbilicus and periphery; axial sculpture of very fine, curved, axial growth-lines. Umbilicus deep, of average width; margin usually roundly angled and at most very weakly pliculated by growth-lines; interior with a variable number of strong to faint spiral lirae. Aperture roundly three-cornered, peristome incomplete; outer lip prosocline, smooth edged; interior nacreous.
Protoconch: Typically solarielline, 380-420 µm in diameter.
Colour: Ground colour yellowish-white overlaid by a very variable pattern in shades of brown; pattern often in form of zig-zag radial stripes frequently fewer, but bolder and broader at and below periphery; sometimes a narrow spiral band of V-shaped marks just below suture, occasionally a second toward periphery; base sometimes only faintly coloured. Protoconch white to pale pink, tip sometimes tinged with greyish-red. Shell generally lustreless, but base occasionally glossy.
Dimensions: Largest specimen (SAM), length 5,6 mm, diameter 8,0 mm.

Compare Spectamen multistriatum. However, this is easily distinguished from I. agulhasensis by its large protoconch, rounded whorl profile and lack of colour pattern; furthermore, its radula has well-developed latero-marginal plates. I. rhyssomphala is also similar, but has a pliculate umbilical margin, darker coloration and occurs further north (Durban).
I. agulhasensis is a variable species in height, strength of sculpture and colour pattern. Western Cape specimens often tend to be larger, more depressed and to have a stronger sculpture than those from Transkei. Not a distinctive species and difficult to diagnose precisely.

South-Africa. South-western Transkei to False Bay, 70-280 m