Shell large, up to 26.20 mm long, moderately arched (length/height ratio 2.27-3.98, mean 3.11, SD 0.53, n = 12), apex weakly inclined anteriorly. Anterior end occupying 25.1-38.2% (mean 35.2, n = 12) of shell length; anterioi slope very weakly convex, lateral and posterior slopes broadly convex. Aperture gently arched from side to side. Wii increasing growth, longitudinal axis gradually twisting roughly 5° anticlockwise between teleoconch I and end of teleoconch II in adults. Teleoconch I depressed conical, length 1.90-2.20 mm (mean 1.95, SD 0.09, n = 12), anterior and pos terior slopes flat to weakly concave, lateral slopes flat, glossy, essentially smooth apart from commarginal growth line; and obscure radial lines. Teleoconch II sculptured with strong radial costae and commarginal ridges, rounded nodules at intersections; fine, crisp, crowded commarginal growth lines throughout. Radial costae rounded, crowded, multiplying by intercalation. Radular teeth (IM-2009-4260, adult) roughly 360 mu long, with 11 cusps. Holotype length 21.2 mm.

Compared with P orientalis Schepman, 1908, which is similar in shape and in attaining large size, P beta n. sp. differs in having a smaller teleoconch I (length 1.90-2.20 mm vs. 2.30-2.60 mm), much more closely spaced and more numerous radial costae and commarginal ridges, with interspaces narrower than each costa and ridge. A single specimen of P orientalis Schepman, 1908 was taken within the geographic and bathymetric range of P beta n. sp. (sympatric), and they may well be locally syntopic. A species with extremely similar shell morphology, P gamma n. sp., is described below. Compared with P obtusa (Thiele, 1925) (holotype and only known specimen 7.00 mm long - adult size unknown: Figures 9G, H) at the same stage of growth, P beta n. sp. differs in having a more elongate P1 and stronger, more widely spaced commarginal ridges and more crowded radial costae.

Papua New Guinea and Solomon Islands