"The valves are extremely delicate and hyaline, slightly higher than long. It is equilateral and strongly inequivalve, the left valve being considerably more convex than the right one. The dorsal edge is straight. The valves are rather smooth at the umbo, where only a fine irregular concentric striation is present. In addition both valves have a fine radiating sculpture and are provided with sharp regular and prominent ribs which gradually develop into rounded undulations towards the periphery. This is particularly the case in the right valve, while in the left valve they retain their character of ribs to a larger degree. Towards the anterior and posterior ends at both the left auricles and right posterior one the undulations become narrow ridges. The auricles just mentioned are not sharply demarcated, while the right anterior one is separated from the disc by a deep furrow with a row of pectinidial teeth. A sharp edge is present between the furrow and the disc. The anterior right auricle has four to five radiating ribs crossed by a somewhat foliaceous concentric sculpture, the junctions of the two sculptures being more or less nodulose. The concentric sculpture causes some serration of the anterior right dorsal edge, but otherwise the remaining dorsal edge is rather smooth. The byssal notch is deep. The resilium rather large, rectangular. The soft parts: The mantle is very thin and membranous. The velum forms an extremely broad lobe ventrally, diminishing rapidly towards both ends. The mantle edge has numerous rather small tentacles and a few long and slender ones reaching the edge of the ventral part of the velum. No velar tentacles arc present. The foot is very small with a rounded sole and a byssal slit. The byssus is well developed, consisting of numerous threads. There is a byssal retractor in each side, the left one being about twice the thickness of the right one. The "quick" part of the adductor is oblique. The areas of insertion of the two sides are approximately equal in size, and about four times the size of the "catch" part. The gills are very large. The mantle edges appear to be symmetrical. No eyes are present." (fide Knudsen, 1970)
Size: Normal adult size range is 15 to 20 mm.
Distribution: Known only from the Kermadec Trench.
Habitat: Deep water, on fine muddy bottoms.