Description: The shell is low patelliform, with the oval aperture, the width being about 80% and the height less than 30% of the length, respectively. The apex is situated at one-third anteriorly, eroded, with small, drop-shaped apical orifice situated slightly anteriorly to the highest point. The shell surface is dirty grayish, and orna¬mented with strong 80-90 radial ribs of various prominency with irregularly intercalated riblets. They are crossed by concentric growth lines that are raised into minute but strong concentric scales thereupon. The apertural margin is finely crenulated in accordance with external ribs that also create shallow radial grooves inside. The internal surface has strong silverly lustre and microscopic, discontinuous concentric lines. The muscle scar is not distinct. The septum behind the orifice is very low, semicircular.
The radula is rhipidoglossate, typical for the family. The central tooth is trapezoid, the inner laterals are slender but similar in shape to the central, and the outer laterals have peculiar flare in the middle of shaft that make them interlocked with each other. The innermost marginal (outermost lateral) is extremely large and robust with broad top which is hook-shaped in profile and carries small denticles and a knob-like lateral cusp. The outer marginals are innumerable in number with fine serration on top.
Remarks: This species is characterized by a very low shell and scale-like sculptures on radial ribs. There is no Japanese fissurellid referrable to such a flat and strongly sculptured species. P. kawamurai HABE, 1961 has much higher shell with smoother ribs. A deepsea species P. regia SHIKAMA & HABE, in HABE, 1961 has also a high shell and finer and more numerous riblets.
Measurements: Holotype (National Science Museum Tokyo, NSMT Mo-69966) length 18.6 mm, width 15.1mm, height 5.5 mm; Paratypes (NSMT Mo-69967 a, b) 17.0x13.5x4.8 mm; 12.8x10.5x3.9 mm.
Distribution: Hitherto known only from the type locality (Izena Hole, 1430 m deep).