Parvamussium kauaium (Dall, Bartsch & Rehder, 1938)
DALL, W. H., P. BARTSCH & H. A. REHDER. 1938. A manual of the Recent and fossil marine pelecypod mollusks of the Hawaiian Islands. Bernice P. Bishop Museum Bulletin, 153: i-iv, 1-233, pls. 1-58. [p. 80, pl. 19, figs. 4-7; pl. 20, figs. 1-2]
1938 Propeamussium kauaium Dall, Bartsch & Rehder, 1938
W. H. Dall, P. Bartsch & H. A. Rehder, 1938, plates 19, 20.
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«Shell small, equivalved, but not equisculptured, white; auricles not quite equal; the anterior considerably larger than the posterior. A slender byssal notch is present at the junction of the anterior auricle with the central portion of the shell. The anterior auricle is marked by seven strong radiating cords which occupy three fifths of the space between the sinus and the summit of the auricle. It is also crossed by many curved cords which grow increasingly stronger from the umbo toward the outer margin. Their junction with the radiating threads forms nodulose scalelike elements. The dorsal portion, however, has the concentric cords much stronger than those ventral to it. The posterior wing of the right valve is almost straight, and is marked by slender concentric cords which are slightly overlapping and which also grow stronger from the umbo to the lateral margin. The disk portion of the shell shows the internal cords as light rays. Its sculpture consists of concentric cords which are very regular and are about as wide as the spaces that separate them. In addition to this, fine microscopic, closely spaced, radiating lirations are present. The left valve has an entirely different external sculptural pattern. The anterior wing is marked by a series of strong lamellae which slant outwardly and which are crossed by nine radiating threads and a tumid area at the dorsal extremity. The threads render the lamellae slightly nodulose. The early post prodissoconch stage of the shell is smooth; the part following is provided with strong, hollow, rounded, concentric cords which become consecutively a little more closely spaced from the dorsal to the ventral margin. These are about one third as wide as the spaces that separate them. In addition to this, there are numerous, closely spaced, radiating threads between the concentric cords which are not quite as wide as the spaces that separate them, thus giving to the surface of the shell a latticed appearance, in which the concentric sculpture, however, is much stronger than the radiating threads. The anterior portion of the dorsal edge of the hinge in the right valve bears fine projecting scales that give it a somewhat tilelike effect. These scales grow stronger from the umbo toward the edge. Immediately below this there is a series of fine denticulations in both valves, both anteriorly and posteriorly. The ligamental pit is triangular; its base forms a little shelf that projects into the body cavity. The disk portion of the interior bears 10 strong radiating ribs. All the external sculpture is visible through the thin texture of the shell.
The type, U.S.N.M. Cat. No. 173218, was dredged by the U. S. Bureau of Fisheries Steamer Albatross at Station 4022 near Kauai in 399-374 fathoms on coral, sand and foraminifera and rock; bottom temperature 41° F. It measures: height, 10 mm.; length, 9.9 mm.; diameter, 2 mm.
This species is easily distinguished from all the other Hawaiian Propeamussiums by its having hollow concentric cords on the left valve.» WILLIAM HEALEY DALL, PAUL BARTSCH & HARALD ALFRED REHDER, 1938
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