Related, at first sight, to Call. zizyphinum, the shell of this species presents, however, « so particular and different characteristics that it can certainly be considered the representative of a form not yet described. » – G. Coen: “Di una nuova forma mediterranea di Calliostoma”, Annali del Museo Civico di Storia Naturale Giacomo Doria vol. 59, Genova 1936, p.272. The author then makes a comparison (p.273) between this new form and that of Call. zizyphinum, from which it appears that the sculpture is distinctive…
 
If, in zizyphinum, only the apical whorls are granulose, in agrigentinum this is the whole shell that bears a very strong spiral sculpture, crossed by some radial striation: « All the whorls, from the apex to the peristome, bear 5 strong spiral cords, of which the 4 upper ones are very and regularly granulose; the lower one being almost – but not completely – smooth. All the intervals between these cords bear a minor secondary intermediate funiculus, completely and minutely granulate. »