Parvamussium nesiotum (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. 81, pl. 19, figs. 12-15; pl. 20, fig. 7]
1938 Propeamussium nesiotum Dall, Bartsch & Rehder, 1938
W. H. Dall, P. Bartsch & H. A. Rehder, 1938, plates 19, 20.
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«Shell very small, gibbous, alabastine. There is a triangular notch formed by the junction of the anterior wing with the central portion of the right valve to form the narrow byssal notch. The wing itself is marked by four rather broad, low, rounded, radiating threads, and posterior to this by a broader area almost as wide as the four ribs. All of the wing is marked by concentric, rather strong lamina which increase in strength from the umbo toward the edge. The posterior wing of the right valve is shorter than that of the left, and is marked by nine very feeble, obsolete, radiating riblets on its ventral half; the posterior half being without radiating ribs. This wing is also marked by concentric lamina which are not as thick as those on the anterior wing but equally prominent. The central disk of the shell of the right valve is marked by concentric lamina which wear down into rounded cords on the early part, but are well elevated ventrally. The laminae adjoining the posterior wing are slightly denticulated, suggesting additional radiating threads here. This, however, does not obtain at the anterior margin of the right valve. The left valve has the anterior wing marked by nine radiating ribs and a broad tumid area posterior to this, the latter occupying about one third of the width of the wing. This wing is marked by strong, rather regular, projecting and outwardly reflexed lamellae. The same sculpture applies to the posterior wing of the left valve, only here the radiating threads are very feeble. The central disk of the left valve is marked by concentric threads and numerous radiating ribs which are of equal strength and which enclose squarish or rectangular pits. The junction of the ribs and concentric threads forms feeble nodules. The interior of the shell is milk-white. The hinge is very narrow and straight. The resilial pit is narrow and small. The disk part of the interior shows 12 radiating ribs.
The type, U.S.N.M. Cat. No. 190441, was dredged by the U. S. Bureau of Fisheries Steamer Albatross at Station 3846 off the south coast of Molokai in 60-64 fathoms on coarse broken shell, sand and gravel bottom; bottom temperature 71.5° F. It measures: height, 4.9 mm.; length, 5.1 mm.; diameter, 3 mm.
The strong radiating ribs of the left valve which here are not hollow, combined with the fact that the anterior wing of the right valve has no radiating ribs, will distinguish it from all the other Hawaiian Propeamussium species.» WILLIAM HEALEY DALL, PAUL BARTSCH & HARALD ALFRED REHDER, 1938
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