Diagnosis. A typical rather small Calliostoma species with an elevated, conical spire, 6 spiral cords with a strong abapical granular spiral cord making keel, the strongest cords with blunt pointed beads, an almost Hat base with 9 thick granular spiral cords and strong axial riblets between them, without umbilicus.
Description. Shell of moderate size for the genus (height up to 11.2 mm, width up to 8.8 mm), higher than wide, conical in shape; spire elevated, height 1.2x to 1.3x width, 3.9x aperture height (holotype only, paratype immature); angulate periphery; anomphalous. Protoconch about 220 µm wide (encrusted on all available specimens), of 1 whorl, rounded, with a network of ridges giving reticulate shape; apical fold more or less straight, without clearly visible terminal varix.
Teleoconch of up to 7.7 whorls; whorls straight, last whorls with a suprasutural keel. Suture poorly visible, not canaliculated. First whorl convex, sculptured by axial, weakly prosocline threads and 3 spiral cords P1, P2 and P3 appearing immediately, all granular by intersection with axial threads; P1 weakest, P3 strongest; P2 closer to P1 than to P3; P4 completely hidden by succeeding whorl; distance between threads 2x larger than threads. At end of second whorl, S3 appearing above suture; S2 absent; distance between axial threads about 2.5x larger than threads. On third whorl, P3 strongest, S3 thickening, as strong as P3; P4 partly visible above suture; beads of cords connected by axial threads giving a reticulate pattern. On fourth whorl, SI appearing, thin; S3 strongest. On fifth whorl, S3 strongest, making keel with sharp pointed, horizontally oriented beads; P1, S1 and P2 similar in size at end of whorl, weaker than P3; axial sculpture weaker. On last whorl, P4 fully visible, peripheral, granular, weaker than other cords; interspace between cords similar in size to cords; a tertiary cords may be present between P1, S1, P2 and P3; axial threads weak (paratype) to nearly obsolete (holotype) except in abapical part.
Aperture roundly subquadrangular; outer lip thin, straight; basal part rounded, producing an angle with outer lip and an more obtuse angle at meeting point with inner lip.
Columella nearly straight, weakly oblique, slightly swollen in the middle, without tooth; callus completely covering umbilicus.
Base weakly convex to almost flat, with 9 or 10 strong, granular cords; interspace between cords similar in size to cords; low, thick spiral threads visible between spiral cords. Colour of teleoconch off-white to light grey; brownish flames or shades may be present; protoconch off-white.

The placement of the new species in Ampullotrochus subgenus is justified by the angulate periphery, the almost flat whorls and the late persistent axial sculpture.
Calliostoma (Ampullotrochus) aporia n. sp. is similar in shape and size for a similar number of whorls to C (Fautor) houbricki Marshall, 1995 from New Caledonia, but this species living at a similar depth shows thin yellowish brown spiral line in the interspaces between spiral cords, has a larger protoconch (350-370 µm) and a subangular (not angulate) periphery.
The new species also resembles C. katsimakamai Kosuge, 1998 from Indonesia, but this similar in size species has a S2 spiral cord and no S3. Calliostoma (Ampullotrochus) aporia n. sp. also resembles C. (Benthastelena) pertinax Marshall, 1995 from New Caledonia, but this similar in size species has a larger protoconch (400 µm), has a S2 (commencing before S3) and a different colour pattern.
The new species somewhat resembles C (Ampullotrochus) alisi Marshall, 1995 from Loyalty Islands, but this slightly larger species has a larger protoconch (430 µm), has a S2 (commencing before S3) and a S3 not prominent. Calliostoma (Ampullotrochus) aporia n. sp. can be compared to C simplex Schepman, 1908 from Indonesia and Philippines, but this slightly larger species has a S2 (commencing before S3), a S1 being the most prominent (not S3) and much thinner spiral cords on the base.
The new species can also be compared to C. (Fautor) belauense Okutani & Kurata, 1998 from Palau Islands, but this much larger species with a similar number of whorls has more numerous spiral cords on the whorls, with S2 present, and more numerous, low, smooth basal spiral cords.

Solomon Islands. 128-150 m.